Reductionism as Negation of the Scientific Spirit
The Problem of Reductionism in Science, Dordrecht 1991
The polemic accent implicit in the title of this essay must be understood as a statement addressed against an absolutization or excess, namely, the absolutization of a methodological approach which, in other respects, is fully legitimate and correct in itself, provided one remains conscious of its conditions of application and limits. This approach is the perspective of reduction, of which «reductionism» (as in general for every «-ism») results in unjustified dogmatic generalization. But, because one may speak of reduction according to different meanings , it would be a difficult task to define reductionism by relying upon the various meanings of the concept of reduction. It is, therefore, easier to characterize the concept of reductionism directly, for it corresponds to an intellectual attitude, a genuine metaphysical vision, which is more fundamental and more ancient than the methodological approaches one could class under the epistemological notion of «reduction» and which, at bottom, is responsible for the very absolutization of which we have just spoken.
Nature of Reductionism
The most general characteristic identifiable in reductionism is that which may be called the elimination of the difference, elimination consisting not so much in a search for that which might be common to two kinds of things, to two types of diversely expressed realities, but rather in claiming that the perceptible difference is but apparent, affirming that, «in reality», one of the two kinds embraces also the other, as one of its possible forms of manifestation. Now, researching what is common to two different realities is one of the most normal intellectual activities. One could say that it is a basic factor in all of our understanding, that which permits us to pass from the pure and simple level of perception to that of concepts; but this does not imply the elimination of the differences. We simply recognize that, beside their diverse traits, things also possess various common traits; we deny nothing of that which experience teaches us, for the common traits themselves are, in a certain manner, attested by experience. To the contrary, when one denies the difference, when one removes from it any character of authentic reality, one becomes engaged in a metaphysical claim: first of all, because one attempts to affirm «what a certain reality is in itself», what is its «essence» (generally «hidden»), and, secondly, because this more profound nature is presented as going beyond the level of experience, even so far as to impose upon experience the implicit accusation of being a source of simple «appearances» (and this, moreover, is, in general, the sign of a poor metaphysics). If we consider many examples of reductionism, such as they are asserted regarding the relations between different sciences (for example, the thesis of the reducibility of psychology to biology, of biology to chemistry, of chemistry to physics) we readily encounter, more or less explicitly, this manner of thinking. 
At first sight, the reductionist tendency, as we have sketched it, seems to be characterized as a (perhaps risky) prolongation of the search for what is common to diverse realities. However, this is not the real issue; reductionism is, more precisely, a particular response which is given to the problem of searching for the unity of multiplicity, that is, the response that monism gives to this question. Of course, the unity of multiplicity is, again, one of the fundamental conditions for the intelligibility of the real, a condition without which one could neither think nor declare, for example, that a certain individual possesses different properties and yet is nonetheless one and not several; or that it is the same individual which has changed place, grown, or suffered from illness, who, in short, manifests himself differently in time, but always remaining the same individual. Now, the simplest solution presenting itself before this difficulty is that of performing such a reductio ad unum by postulating the existence of a unique kind of stuff, of some fundamental underlying substance, of which everything existing should be but a different manner of presentation, of appearance.
The first Greek philosophers actually began by proposing their world interpretation from this point of view, and monism has never failed since to manifest itself throughout history to the present day. That which has changed has simply been the identification of the said ultimate stuff, or fundamental substance, whose properties should suffice to explain all the differences that experience attests to us in that which exists. This stuff does not need to be conceived as a particular type of matter: it can be as well indicated in the Spirit, as was the case for the idealists who claimed to reduce matter to spirit, rather than spirit to matter. But that which has always remained unsatisfying in every form of monism is the real ostension of how that which is one can give rise to diversity, to plurality. This same difficulty unmercifully confronts as well the different forms of reductionism upheld in the scientific domain.
In order to avoid the difficulties of monism, the perspective of pluralism was introduced in philosophy at a relatively early stage, that is, the admission of a certain number of basic constituents of the universe, whose infinitely variable combinations, due to the influence of certain causes, would account, in principle, for the multiplicity of beings. This solution eliminates the difficulties proper to monism, but still lacks the strength to resolve the problem of the unity of multiplicity. Indeed, even if the fundamental elements are few, the problem of understanding how they combine to give rise to concrete beings with all their differences remains unsettled, for this problem cannot be solved by a simple juxtaposition of different constituents taken in variable proportions, but demands the explanation of their differentiated organization, to which also corresponds the appearance of highly differentiated properties. But there is another possible difficulty. Pluralism ultimately suffers from the same weaknesses as monism, if it fails to arrive at admitting a true ontological diversification, for if the fundamental elements, while individually distinct, are conceived as belonging to the same kind of reality, one abides in the presence of a masked monism. True pluralism demands that one admits of a number of constituents of the real sufficient to account for all the differences that reality shows, differences with regard to which one does not have the right to impose ontological limitations a priori.
This is why, therefore, the search for what is common does not necessarily lead to the negation of the difference, and the search for unity is neither satisfied via this negation. A confirmation of this fact comes from the consideration of the concept which has been able to lend itself in probably the most efficacious manner to the satisfaction of these two demands, the concept of being. Being appears as the most general of concepts and, at the same time, as the most powerful principle for the unification of the real. Nevertheless, the best representatives of the metaphysics of being have never ignored that being, as Aristotle already remarks, is said in several fashions, that it is an analogical concept, which means that there are real differences within the sphere of being, that all beings do not have the same ontological status, hence, that the notion of being itself does not permit us to reduce the beings of a certain ontological level to that of another. (The notion of being neither results in an elimination of differences, one of the fundamental reasons, moreover, for which it is so precious).
That which we have just laid down, to the extent that it exposes the reasons for the intellectual fascination of monism and highlights at the same time its profound insufficiencies, helps us to understand why and how in the domain of the sciences reductionism was able to develop. This latter is a kind of applied monism, that is, a monism delimited to the scientific field: apparently it advances no metaphysical pretension and is limited to bearing among the sciences the demand of generality and of unity. However, it is exactly the manner in which the satisfaction of these demands is sought that denounces its surreptitiously metaphysical character, as we have already established and will again have the occasion to verify. But we would like first to see how the very project of reductionism finds itself in conflict with the intellectual attitudes having permitted the constitution of modern science.
Some Characteristics of Scientific Knowledge
«Modern» science, in the usual sense of the term, is that which was constituted in the 17th century as the science of Nature, according to the adoption of an intellectual approach which was delineated and applied in an explicit and conscious way, in all of its fundamental elements, especially since Galileo. Amongst the new traits distinctively characterizing this science, with relation to the previous attitude with which one studied Nature, are the following.
i) The knowledge of natural objects does not aim at the penetration and grasping of their intrinsic «essence», but is satisfied to study a certain number of their «affections», that is, a certain number of their properties, which lend themselves to being isolated and relatively simply described along with the help of mathematical language. This means, on the one hand, that every hypothesis concerning structures or hidden properties attached to the sphere of observable phenomena must remain foreign to this knowledge of Nature, and, on the other hand, that this knowledge no longer displays the pretension of being exhaustive, of covering the entirety of what is true of a natural object with which it is concerned. In other words, the «affections» that it studies correspond to certain very delimited points of view that one opens upon natural things, without any pretension that the properties that one is able to grasp from these points of view be the most «essential», or that they be the only ones subsisting in the object and that one can study.
ii) Knowledge of the universal is not the precondition for knowledge of the particular, it is not the source from which one is able by deduction or application to expose the actual properties manifested by concrete events. Hence the search for what is common appears to be of secondary importance with respect to the exact determination of that which can be described in detail.
iii) An adequate knowledge of the parts does not necessitate knowledge of the whole. Here we are not referring, as in the preceding case, to the fact of subsuming the particular instance in the framework of concepts and principles of a general order, but rather to the fact of no longer considering as indispensable to the understanding of a particular event the reconstruction of its relations with the rest of the world, its insertion into a more complex context. One began to think rather the contrary, namely that the understanding of an event is found in a deconstruction of the event, in exposing the parts from which it «results» and their way of functioning.
Delimitation of the Field as the Condition for Scientificity
The three characteristics we just sketched, after having determined the intellectual style of physics, have expanded little by little to the point of covering (with the necessary adaptations) the entire domain of the science of Nature, and finally the entire sphere of scientificity in general. Already at first sight, we note that the first two of the mentioned characteristics respond to an attitude opposed to that which we uncovered at the base of reductionism. In fact, they express the renunciation of this primary aspiration toward generality, of this search for the essence and ultimate explanations, which are typical of philosophical thought in its metaphysical aspect, and which have therefore authorized us to qualify the attitude of reductionism as «metaphysical». As regards the third trait, it may be considered as the conceptual root of the method of reduction, and the fact that it may be taken as one of the distinctive traits of scientific knowledge, while reductionism appears to be contrary to it, already tells us that reductionism and reduction must not be confused. But in order to better analyze these questions it would befit us to examine in greater detail the sense of the demands expressed in the first two characteristics, sense which we synthetically designate here as the proposal of a conscious delimitation of the domain of investigation.
The existence of such a delimitation as a distinctive trait of scientific research is something well known, and corresponds to the idea of specialization, universally recognized today as a necessary condition for this research. Nevertheless, one tends to think that specialization is a sort of necessary evil imposed upon us by quantitative reasons, that is to say, because the volume and extension of scientific knowledge in every discipline have become so enormous that no human individual is capable of mastering them all, whence the obligation that each person limit himself to cultivating and penetrating a single limited sector. Without denying what is true in this justification of specialization, we must add another which is less contingent and more structural: it directly proceeds from the Galilean program we evoked above and consists in limiting oneself, in the study of things, to the mere consideration of certain «affections», or aspects, or properties. And here lies the veritable core of specialization. The specialist is not he who knows only a very limited number of things (this would lead us to say that the ignorant man is the best specialist), but he who knows the greatest number of things within a delimited sector, that is to say, concerning a certain aspect of the real.
It is by thoroughly investigating this awareness, and by explicitating its conditions of application, that we arrive at a satisfactory characterization of the very idea of scientific objectivity. Having already accomplished this work on other occasions, we shall not repeat ourselves here, and we shall simply recall the essential results of this explicitation: 
(i) every scientific discipline (as well as every specialized sector within a discipline) is characterized by a point of view from which it considers reality;
(ii) the adopted point of view leads one to consider as objects of a discipline only those aspects of a thing accessible to that point of view;
(iii) the adopted point of view has to spell itself out in a number of specific concepts which become the technical predicates of the discipline in question, and whose meaning is strictly dependent upon the disciplinary context within which they fall;
(iv) among these predicates, there must be some which are connected with concrete operations, in virtue of which one can effectively apply the chosen point of view to the study of reality and discern whether what one affirms is true or false;
(v) thus constituted, the ensemble of predicates determines the type of objects with which a discipline is concerned and, in particular, the operations characterizing certain predicates determine the ontological status of these objects;
(vi) it follows that a single term, used in two different disciplinary contexts, receives, within the two, different meanings and refers to different types of objects;
(vii) the same thing may become the object of investigation for several different disciplines, to the extent that it lends itself to being investigated from different points of view, or (equivalently) to the extent that it possesses properties of differing nature;
(viii) none of these possible «objectivations» exhausts the thing, exactly as each objectivation corresponds to a determinate point of view, and there is an indeterminate number (even potentially infinite) of other possible points of view.
If we may consider the preceding propositions as an acceptable characterization of the modern scientific attitude or spirit, in its concern for objectivity and rigor, we can conclude that reductionism is quite opposed to such a spirit. Indeed, these propositions constitute a veritable canonization of the difference, and make of the explicitation of the differences and specificities the basic condition for the construction of the scientific discourse. From this point of view, reductionism is unable to appear otherwise than the result of two possible equivocations: either the equivocation consisting in believing that one can speak about objects belonging to a certain domain in the discourse of a discipline concerned with other objects, or the equivocation consisting in believing that a determinate discipline can attain knowledge of the thing in its totality. The two alternatives are incompatible with the structure of scientific objectivity. The first is excluded by the fact that the predicates of a discipline determine and «construct» (by a sort of «clipping out» of things) the objects of the discipline, in such a way that these predicates are rendered constitutively incapable of speaking of «other objects» and, therefore, of «incorporating» them into their proper discipline. The most that we could expect is that the two disciplines admit of operations in common, permitting them to refer to the same things, but it always remains the case that they envisage and study different aspects in these things.
The second alternative is excluded by the fact that no investigation exhausts the «thing»: the only way to avoid this difficulty is to say that the discipline to which one wants to reduce the other or others is that which attains to the essential aspects of the thing or of reality, but, in this way, this discipline is made a metaphysics and no longer a science. In no way, then, can reductionism be reconciled with the scientific spirit.
Reduction and the Analytic Method
We return now to the third characteristic of modern science, which we sketched above as being a kind of reversal of the conditions for the intelligibility of the real. While the classical tradition sought the comprehension of a thing, of a property, of an event in the possibility of situating them as elements or parts within a whole - in a totality already known and supplied with a sense - interior to which one could reconstruct the reasons for their existence and form of being, the new scientific perspective seeks this comprehension and this explanation, on the contrary, in the deconstruction of the same realities. It is these which are conceived as the totality and the whole, and one hopes to understand them through the laying out of their parts, through the observation of the manner in which these parts function, and by showing that the constitution, the properties and behavior of our (tiny) «whole» results from these aspects of its parts. In this consists the characterizing feature of what may be called the analytic method.
One could make several interesting observations with regard to this intellectual attitude: we shall limit ourselves to some very brief considerations. In the first place, one recognizes here a sort of unconscious disguise of the ancient aspiration to investigate the essence of things. This essence came, little by little, to be conceived as a hidden core, like an «intimate» substratum found in the interior of the thing, above or beneath the «affections» and its visible properties. The «intelligibility» of a thing was therefore conceived as an intus-legere, as a «reading inside», which was esteemed realizable thanks to a precisely «intellectual» act capable of seizing the hidden qualities susceptible to producing by a causal action the visible manifestations. Now this idea of «seeing inside» is found again in the idea of deconstruction of which we have just spoken, but in a sense which is no longer speculative or purely intellectual, but rather empirical and concrete, a bit like the child who breaks his toy in order to see what is inside. One might wonder why men had converted to this new approach, and the response (or at least a plausible response, that can be drawn from the texts of authors of that epoch) is that entire centuries had shown the sterility of the efforts to advance the knowledge of particular natural realities by means of deductions performed from the great principles supposed to assure the intelligibility of the world in its entirety, and hence applicable as well to its parts. Instead of grounding the inquiry upon the «first principles», it was hoped to better take advantage of the knowledge of certain «first realities», namely, concrete realities entering into the constitution of things falling within the sphere of our ordinary experience.
There is something more profound in this perspectival change. According to the preceding point of view, the growth of knowledge is realized by an amplification of that which is already known and which constitutes a sort of guarantee of the truth of that which one is going to add to that, for this latter must in some fashion «flow» from (or at least be compatible with) what one already knows. On the contrary, within the new perspective, the understanding of that which is already known is awaited from the discovery of that which one doesn't yet know. No one knows in advance what the analysis will reveal to us, and the intelligibility of the world depends no longer essentially upon reason but rather upon experience, subsequent experience, which, being unforeseeable, could even place into question that which we have up to present considered as known.
The simple presentation of this perspectival change suffices to make us appreciate the formidable charge it contained from the point of view of the progress of knowledge and to make us understand the new spirit which inspires it. It is the spirit of discovery, the fascination with the unknown, the search for what is new. The analytical method imposed itself not only as the fundamental method of science, but also as the intellectual style of modernity: if scientists have proceeded to a more and more elaborate dissectio naturae in using more and more detailed and particular «points of view», and more and more differentiated and technically refined methods of observation, the philosophers have concerned themselves with uncovering the «simple», «clear» and «distinct» ideas upon which they could build a knowledge endowed with certitude, and the mathematicians have applied themselves to the invention of instruments for the «analysis» of geometric space, of the infinitely great and of the infinitely small.
If we accept naming «reduction» the application of this analytical method (which is legitimate), we can affirm that the unprecedented success that the application of this method has assured in every domain of knowledge throughout the course of three centuries justifies to a large extent the high esteem that this approach enjoys. Nevertheless, we must more deeply examine the question in order to correctly evaluate the nature and import of these merits.
Reduction and Explanation
What is undeniable is the fact that the adoption of the reductive method has procured for us an enormous mass of knowledge as regards the different sets of «parts». If we want to use the same image already introduced, we can say that the adoption of this method has procured for us an unsuspected quantity of information concerning the «internal layers» of many realities which before were known to us only at their most «superficial» layer. If we take resource to another image (which is also widespread), which calls «inferior levels» that which one attains in deepening the analysis (namely, the levels to which belong the parts or components), we can say that the adoption of this method has opened for us a very rich understanding of these inferior levels. But the question now emerging is more complex: can we affirm that this augmentation of knowledge has permitted us to better understand the initial phenomena, namely, the phenomena of the superficial layer or of the superior level? The response depends evidently enough upon what we mean by «understanding».
The most direct sense of this notion refers to the meaning of concepts (and by this intermediary to the meaning of propositions). Now, it appears difficult to maintain that the concepts of the superior level had no meaning before the analysis or reduction, i.e., that we were unable to understand them. If indeed one had not understood them, if one truly didn't know what they meant, one would never have been able to «analyze» them and achieve any discovery of the inferior layer. Therefore, the idea of «understanding» must be conceived of in a more indirect and general sense, a sense one could express in saying that to understand something means «to attain an awareness of how it is». From this point of view, all new information capable of being obtained increases our understanding, for it reveals to us relations, connections, concomitances of which we previously had no precise idea: it is capable of enriching the meaning of the concepts at our disposal, without however changing it. This is why the use of a locution such as «superficial» layer runs the risk of producing misunderstandings: we are in a habit of attributing a negative connotation to this adjective, whereas, if we limit ourselves to an account of the simple idea of «progression» which it indicates, we can more correctly say that the «superficial» meaning is correct within its domain of specification. Reduction, therefore, increases our understanding in the sense just specified.
One attributes sometimes to the notion of understanding a more engaging meaning, after which to understand something means «to know why it is what it is». Now in this case it is more opportune to speak of explanation. In ordinary language these two concepts are used practically as synonyms, but in a more rigorous discourse it is good to distinguish them and to reserve the notion of explanation to the specific task of «supplying the why». Of course, even the notion of «supplying the why» is far from being conceived in a univocal manner, although in the epistemology of the sciences one practically accepts that the ostension of this why consists in the performance of a correct deduction. But deduction from what?
Here we encounter what is perhaps the most fundamental difference between the traditional approach and the analytic one. The traditional approach regarded the explanation of an object, of its properties and its behavior, as the possibility to deduce them from the «whole» within which it is comprised, and from the principles governing this whole and giving an order and logical connection to its parts. The analytic approach conceives explanation as a deduction beginning from the constituents and the laws which govern the relations between them. We have seen that the traditional approach had not enjoyed a great success in its efforts to explain the particular from the whole, and we must now ask ourselves if the analytic (or reductive) approach enjoys greater success. The thesis according to which this approach is effectively successful can conventionally be called epistemological reductionism. Is this a well founded thesis?
In order for a deduction such as it is implied by epistemological reductionism to be correctly possible, it is first of all necessary that there be a conceptual reduction, that is, it is necessary to be able to translate without residual the concepts of the superior level as functions of those of the inferior level. Next, it is necessary that all the true propositions of the superior level be transformed into theorems within the theory that describes the phenomena of the inferior level. These conditions are not easy to realize, and already from a formal logical point of view there are some well known limitations to this. However this is not in principle impossible, and an example that one could mention is probably that of the reduction of optics to electromagnetism: this «thing» which is light, and which was already «objectified» thanks to the concepts of the luminous ray and its properties in traditional optics, translates itself without residuals in the electromagnetic theory of light. Already much more complicated and controversial is the case of the possibility of reducing thermodynamics to the kinetic theory of matter.
In the case of other reductions usually proposed, the thesis of epistemological reductionism becomes more and more problematic and even false (reduction of chemistry to physics, of biology to chemistry, of psychology to biology, etc.). For example, despite all the progress of molecular biology and biochemistry, one is not in a position to remedy the absence of biological concepts in the vocabulary of chemistry, nor to give truly exhaustive definitions of the fundamental biological notions in chemical terms, which is preliminary to every enterprise which could translate all true biological propositions in as many theorems of chemistry. That which is actually being done is the assumption of the biological phenomena as a field of «things» to which the criteria of objectivation proper to chemistry are applied. This leads us to discover a whole series of chemical aspects of biological phenomena, but this does not yet mean reduction.
Our last affirmation permits us to say that epistemological reductionism, while not supportable as an absolute position, has the right to be applied at the interior of every discipline, in the following sense. Every discipline has the right to strive to read according to its criteria of objectivation any dimension of the real: the result of this effort will always be positive, for it will lead us to discover an ever more rich quantity of aspects, of constituents, of factors relevant to this discipline which are effectively present in the world. What is essential is that this unlimited effort not be transformed into the pretension of having thus eliminated the differences, of having erased the other points of view and fields of objectivation which derive therefrom. If one gets beyond this limit, one falls within the anti-scientific attitude we have already illustrated, and which consists exactly in the disregarding of the conditions of delimitation founding the very notion of scientific objectivity.
What is the hidden reason which promotes in general such a tendency to exceed the limits? We have already indicated it: it is ontological reductionism, the conception according to which there exists one single fundamental stuff of the world and that, therefore, the science which concerns itself with this fundamental stuff will arrive sooner or later to encompass the other disciplines concerned only with certain «manifestations» or more «superficial» properties of this stuff. We have already denounced the arbitrary metaphysical character of this conception, but we are now able to better see its illegitimacy from the philosophical and scientific point of view.
From the philosophical point of view, this conception introduces an arbitrary separation between the substance and its properties. Now, a substance is not something indeterminate and mysterious to which the properties are «added» or cling. A substance is the ensemble of its properties, and it is differentiated from other substances precisely because it possesses ontologically different properties, as likewise it may belong to the same genus as other substances if it possesses ontologically the same properties as these others, and if these properties are those which have been chosen to define the genus. Scientific objects realize this condition, so to speak, in the pure state, for they are entirely and exclusively defined by properties which explicitly characterize them and which are studied by the discipline concerned with them. Now, a discipline would be able to exhaust the discourse on a given substance only if this substance possessed exclusively the properties with which this discipline is concerned, which is impossible for at least two reasons. First of all, because a scientific discipline (as we have seen) treats only of a delimited number, generally very small, of properties of things, whereas the concrete substances (that is, the «things») effectively possess many more. In second place, because, among the properties that one attributes to things, and which can therefore be investigated by a discipline, there are several which do not belong to the substance «in itself», but insofar as it is found in relation with other substances, relations which, from the simple knowledge of «intrinsic» properties, are not predictable (and therefore unknowable). Finally, because a great number of properties can be attributed to things according to the «points of view» we open upon them, and these properties are again indefinite in number and unforeseeable. This is why, even admitting that a discipline be able to exhaust the properties that a substance possesses «in itself», it could never be able to master the properties arising from the two other types of relation that we have mentioned here. For example, even in the case of a tiny piece of gold, for which one might think that the description of its «intrinsic» properties is entirely furnished by physics and chemistry, one will not come to establish, physically and chemically, why it has a certain price on the market, a feature which makes it enter into the sphere of competence of the science of economics. Now, reductionist monism cultivates, in an implicit manner, the absurd persuasion that there is but one sole type of substance in the world, characterized by a small ensemble of properties whose study it attributes to a «fundamental» science, while the others would only be apparent properties added to this substance in an accidental way, and which can be «reduced» (in the sense of being ontologically eliminated) by a research which makes them «result» like appearances tied to the superficial state of our knowledge. The world, on the contrary, is full of very different substances (that is: there is not one sole genus of things), each one characterized by its properties, in part intrinsic, in part dependent upon the relations which they maintain with other substances, and the various disciplines attempt to study them according to limited points of view, each one occupied with only certain properties.
The preceding considerations also show us why ontological reductionism is even more untenable from a scientific point of view: taken seriously, it would mean renouncing to science in order to return to an arbitrary metaphysics, to a metaphysics which pretends to already know what is the authentic essence of things upon the basis of a partial analytical cutting-out promoted to the rank of a key for the reading of the whole. Now, even if one were willing to concede from the philosophico-metaphysical point of view that there is one sole genus of substance, this would not eliminate the legitimacy of attributing to specific and reciprocally irreducible investigations the study of properties that one attributes to substances as a function of their different kinds of mutual relations, there included the relations with the knowing subjects which consider them according to particular points of view.
Reductionism has been contested not only in recent times: already in the past century it was often admitted that the ontological monism which it implies is too heavy a metaphysical presupposition. Nevertheless, the necessity was put forward of a seemingly more neutral reductionism, which may be described in the following way. Let us well admit that each discipline busies itself with its specific objects. Nonetheless, we want to distinguish the disciplines that treat of their objects in a scientific manner from those which do so in a non-scientific manner. What does it mean to attribute to a discipline the honorable qualification «science»? The response has been: this discipline must be modeled after the sciences which have already merited this title, namely, after the natural sciences. This condition, in its own turn, has been explicitated in two different ways: certain authors have conceived it within the framework of epistemic reductionism, that is, in the sense that a discipline becomes scientific from the moment that it is reduced, practically, to a chapter of a natural science and, in particular, of physics, such a reduction furnishing, so to speak, a criterion for measuring the «degree of scientificity» it was capable of attaining. According to this perspective, chemistry is a bit less scientific than physics, but already well advanced upon the right path, biology - to the extent that it is inclined to be reduced to chemistry and, by this bias, to physics - appears to have good hopes to be capable of arriving some day at being strictly scientific, psychology is still quite far from this ideal, but if it should prove capable of being reduced to biology (and by this bias to chemistry and physics) it will have attained fully scientific status. And the other disciplines, such as history, law, economics, linguistics, sociology? The response has been: well, if they cannot satisfy these conditions, they shall remain outside of the frame of the sciences, though they retain interest in so far as forms of the cultural activity of men, beside the arts, morality and religion.
Another position, more tolerant and «liberal», has nevertheless manifested itself. According to this position, to be scientific, one no longer demands of a discipline that it be able to become a chapter of a natural science; it is sufficient that it adopt the methods of these sciences, that it be constructed after the experimental method, that it use instruments of measure, that its concepts be translated in a series of measurable magnitudes, that it have complete recourse to mathematization, that its explanations take the form of deductions performed from general laws, that it be in a position to offer verifiable predictions. Clearly, we can call methodological reductionism the ensemble of conditions here layed-out. But does this represent a legitimate pretension?
Against all appearances of plausibility, this pretension is not legitimate. In reality it disregards that every science is specifically occupied with its specific objects and that these objects are a structured ensemble of predicates dependent upon an explicitly adopted point of view. Now, it can sometimes happen that these predicates are able to satisfy the relatively complex mathematical conditions permitting us to translate them into magnitudes, but this is not obligatory, and if this is not the case, one can no longer pretend that these sciences adopt a genuine mathematization, that they express their propositions and their laws in the form of equations and disequations, that the pertinent deductions assume the form of calculations. Of course, we shall have the right to demand that these sciences offer criteria of objectivity and rigor, but these criteria depend on the nature of their objects. One should demand that they permit the testing of their affirmations, but this does not imply that the tests be exactly of the experimental type; they will have to furnish explanations by means of correct arguments, but this does not impose in advance the kind of deduction and logic that they must employ. In brief, while fully admitting that there is a certain «normativity» in the activity of scientific research, one must see to it that it emerges from the domain of investigation in concern, and one can not erect a method, which has been successful in a domain, as an obligatory normative criterion for all sciences: without falling into a «methodological anarchism», a «methodological pluralism» appears just as reasonable as the ontological pluralism and the epistemological pluralism we have defended up to here. 
The Category of Complexity
A certain number of the reasons we have here exposed against reductionism have already had the occasion to manifest themselves in the bosom of the science which is habitually supposed to offer us the base of all reduction, namely, physics. The crisis of the so called «classical» physics has shown that the concepts and the laws used for the edification of this physics were not everywhere applicable, which is to say that, even interior to physics, reductionism does not function. This fact has sometimes been expressed by saying that the concepts and laws valid for the world of «macro-objects» turned out not to be extendable to «micro-objects». Even if the notion of object employed in these locutions lacks the technical sense that we have given it in our context, it is all the same significant that one make allusion to it.
The reason which has led to a recognition of this change of objects is essentially the taking into consideration of the change of the orders of magnitude, which was at first considered in so far as a passage toward the «infinitely small», and which today has readily been recognized to be essential also when one proceeds toward the «infinitely large», that is to say, when our research objects are situated at the level of cosmic distances and time. But there are not only these two, so to speak, «categorial» differences: a third which becomes more and more clear is the difference in the orders of complexity: that which is valid when one treats of a simple object can easily no longer be valid when one passes to the consideration of a complex system. A rather vague perception of this problem has already existed for a long time: when we learned in school the first rudimentaries of chemistry, we were made aware of the difference between chemical «mixtures» and «combinations». In a mixture, each constituent retains all of its properties and the properties of the mixture are in a certain manner the sum or the «resultant» of the properties of the constituents (pharmaceutical research still aims today at producing such mixtures). To the contrary, in a combination one obtains a new substance, which has completely new properties with respect to the properties of the constituent substances (we see here that the notion of substance that we have used above is far from being a sort of archaism drawn from scholastic philosophy). Classical example, water, which possesses different properties from those of hydrogen and oxygen. Similarly, biologists have for a long time stressed that the properties, reactions and behaviours of a cell, of a tissue, of a colony of microorganisms, studied in vitro can be very different from those which they manifest in the interior of an organism.
Like the notion of order of magnitude, that of complexity is relative and not absolute. A grain of sand is infinitely small with respect to a mountain and infinitely large with respect to the molecules which constitute it. The solar system is infinitely large with respect to a mountain and infinitely small with respect to galactic systems. In a similar fashion, a tissue is a simple element with respect to the organism, but it is complex with respect to the cells which constitute it, and the organism is a simple element with respect to its ecosystem, just as the cell is a complex system with respect to its chemical constituents. We see then that in each of these notions enters the notion of relation. It is as a function of certain relations that we qualify an object as large or small, as simple or complex. Nevertheless, in the case of orders of magnitude, the relations are purely quantitative, whereas in the case of complexity they are by nature qualitative: when we say that the organism is more complex than the cell, we do not want only to indicate that the organism is «larger» (and that therefore this confers upon it certain properties which the cell has not), but that there well exist reciprocal relations between the different cells which are not the same as those which they maintain between themselves within an in vitro culture (case where the pure aspect of the quantitative difference would be taken into consideration); we want to underscore that the organism has certain properties because its cells are organized in a certain manner, which, in particular, modifies their properties and their behavior with respect to that which they do when isolated and even when they are simply «together» in a culture.
The term employed today to distinguish these types of considerations is that of systems, and «systems theory» is just that discipline which has developed the theoretical and practical aspects tied to this point of view, and which one could rightly credit with the merit of having tried to give a scientific status to the notion of complexity.
At first sight, one could contest this affirmation in remarking that, in reality, every traditional handbook of rational mechanics, after having devoted the necessary attention to «point mechanics», passed to the study of «system mechanics», which was developed as an application or extension of point mechanics, without need to introduce new concepts, laws or principles. The «system» was conceived as an ensemble of points and its properties resulted by addition upon these points (addition expressed by means of summations in the case of discrete systems and integrals in the case of continuous systems). Despite all of this, it does not seem arbitrary to affirm that, if one closely regards this type of theorization, one finds there such a quantity of simplifying hypotheses and idealizations, that they lead to the ignoring of the effective description of the concretely acting forces internal to the system and of those which act upon the system from the exterior (which are practically reduced to the consideration of their anonymous «resultants»). Concretely speaking, the actual system of which one rigorously treats in classical mechanics is that constituted of two points subject to gravitational attraction, and one knows well that from the moment that one passes to the treatment of the problem of «three bodies» this mechanics is already confronted with unavoidable difficulties (and this in being limited to the consideration of a single type of interaction, namely, gravitational interaction). Another indication in the same sense comes to us from the consideration of thermodynamics: it is well known that the second principle of this theory, the principle of increasing entropy, is applicable to closed systems and upon this basis it has been possible to correctly affirm that every alleged exception to this principle, which was raised in considering the thermodynamics of living beings, has no force, for these do not constitute closed systems. Nonetheless, one has the right to use this same reasoning to affirm that (precisely because of this non-closedness) thermodynamics is not sufficient to treat of living beings, for it does not attain the level of complexity which objectively characterizes them.
The Search for Unity
Amongst the intellectual demands that have supported the reductionist perspective, we have already had the occasion of mentioning the search for the unity of multiplicity and we recognized that this is a legitimate demand. Have we now come to contradict this affirmation? Not necessarily: it is a question of knowing whether monism is the only possible solution to this problem. In effect, it is not so. We certainly do not want to deny that, in certain cases, the actual finding of a «common root» constitutes an objective and valid step for the partial solution to this problem, but it is not a generalizable solution. However, the considerations we have made are already sufficient to indicate to us other itineraries. The example of living organisms is already there to orient us: each organism effectively constitutes a unity, but a unity which does not deny the difference and which is even assured by the existence of the difference. If the human organism contained but brains, or kidneys, or lungs, it could not subsist: its existence as an individual entity consists in the fact that it realize an organized and finalized synthesis of different parts. If we do not fear using old notions, we can say that the unity is guaranteed by the form, in the profound Aristotelian sense of this concept, which means at the same time an ontological criterion of specificity, a factor of organization, and of functional and finalized coordination. If we choose to remain within the framework of Aristotelian terminology, we can say that reductionism cultivates the illusion that unity can be found in matter, whereas this represents precisely that which is not organized, that which is not a unity but must still receive its unification through forms. The entire swarm of substances which organic chemistry treats are constituted by a number of chemical elements that we can count on the fingers of two hands: they constitute the «matter» which, organized in different manners, gives rise to an enormous number of different organic molecules with their very diverse properties. Amongst these molecules, only a small part enters into the constitution of living matter: they are the «matter» which, again organized in very different manners, gives rise to the diverse types of cells, which in their turn are organized in the tissues and organs of organisms and so on.
Beside this way, there is another which permits the achievement of unification of multiplicity: this one attempts to find the general concepts and principles having an application in the difference, without ever suppressing it. The concepts of being, change, cause, for example, are of this type. If we use the notion of being in order to distinguish that which exists from that which does not exist, we do not claim that every being is of the same genus; if we use the notion of cause to indicate a certain type of relation between events, we are not obliged to ignore the infinity of causes which act concretely in the different types of events and so on. Moreover, a metaphysician is not obliged to imagine being as a sort of preliminary base from which arise the diverse forms of that which exists: one is not obliged to say that «first of all there is being» and then come the beings of a certain kind, and then the beings of another kind, which so appear on account of a more or less mysterious mechanism. Certainly, there are monist metaphysicians who think more or less in this way, but there are also other metaphysicians who do not follow this path. For example, even a metaphysics which admits the existence of a supreme entity that is the first cause of all that exists, affirms that this being is particular, that it is different from other existing realities, that one applies to it the notion of being in an analogical sense, just as it is analogically applied to other realities; equally, the causal act through which one attributes to this entity the creation of the world is specific and particular, different from the causality by which, for example, the artist produces his work. In brief, neither the unification which is accomplished in considering the forms unifying the multiplicity, nor the unification accomplished in using general concepts and principles, eliminates the differences and, notably, the ontological differences.
On What There Is
Spontaneous human understanding is implicitly convinced of the existence of this multiplicity of «ontological regions»: we think it is possible to speak with truth about trees and rocks, but also about our dreams, about numbers and mathematical functions, about our feelings, about characters from a novel, and so on. The various sciences, precisely on account of their specialization, can be considered as a very efficacious way by which man deepens his understanding in some sector of these different ontological regions. Reductionism, as we have seen, due to its monist tendency, goes against this ontological pluralism. Up to now, we have tried to understand the reason for this tendency in attributing it essentially to the desire to discover unity within the multiplicity of what exists, but the more decisive reason is probably more profound: it rests upon a certain fundamental conviction about «what really exists», a conviction which produces as a consequence the attempt to evacuate certain usually admitted forms of existence, which one wants to exclude from the domain of that which «really exists».
Every man and, in a certain sense, every culture, possesses its Weltanschauung, its vision of the world and of things, of which the most fundamental stratum concerns what does exist. There are many things of which the existence is accepted without problem (material things which strike our senses in everyday experience), but there are others for which the acceptance is very variable. For example, there were and there are cultures within which one easily admits the existence of invisible beings which populate the world around us (animism). There were ages where people admitted almost universally the existence of supernatural beings like angels and demons and attributed to them the possibility of having commerce with humans; or again men normally admitted the existence of astral influences upon human affairs and the destiny of persons. In those ages, people believed in good faith that it was possible to prove that a woman was a witch having commerce with the devil and condemn her, and it was thought that astrology is feasible as an exact science. Today, the majority of people belonging to cultures most profoundly influenced by science no longer admit such kinds of existences and, therefore, any reasoning and any evidence invoked to prove to them that a woman is a witch fails to succeed to convince them: for this reason, one would reject as impostures or hallucinations every «empirical witness» put forth as a proof of this fact, and one would look for «natural» explanations (biological, psychological or other) for those facts which could be undeniable. All this because, in the ontology of our contemporaries, there is, in general, no more space for evil spirits or at least for the type of influence of which they had before been esteemed capable.
This reduction of ontological spaces responds in part to a principle of rationality that is sometimes designated as Occam's razor (one should not multiply entities without necessity) and for another part is the consequence of certain ontological «economies», which the development of the sciences has shown to be judicious. Nevertheless, there is also a kind of counterpart of Occam's razor, which can be formulated as follows: one should not eliminate beings without necessity. Now, reductionism sins against this principle insofar as it has the tendency to eliminate ontological regions with regard to which there exists a preconceived aversion. If one begins with the presupposition that life does not correspond to something superior with respect to inanimate matter, if one begins from the presupposition that the intelligence is not something superior with respect to matter, one intends to prove that, and estimates that should be able to do it: reduction, then, appears as a way to successfully implement this program and no failure is able to make one desist from this purpose, for he will say that, in principle, reduction is possible, but that we still need time and research in order to complete it.
Now, as Occam's principle stands on guard against a type of dogmatism (the dogmatism of the unreasonable multiplication of ontological regions), its counterpart is also on guard against another form of dogmatism: the dogmatism of the unreasonable restriction of ontological regions. Moreover, the history of science offers us positive examples of the application of these two principles: for a long time people had believed in the existence of flogiston and of ether and then they were eliminated from the ontology of physics; during a certain period, many scientists opposed the existence of the electromagnetic field and of the atoms, but, in the end, these were admitted in the ontology of physics. The negative examples tied to the ignorance of these two principles are more persuasive if one takes them in the history of humanity: there were ages when people believed in the existence of «ontologically superior» men (kings of divine right, for example) and thanks to this amplification of ontology within the human sphere a legitimate right over the life and death of the other purely human beings was attributed to them; in more recent times, there has been the pretension to completely eliminate certain human beings from the class of men (Jews, embryos, handicapped) and from this reduction of the ontology of the human sphere has been drawn the conclusion that they may be treated as animals and even suppressed without any moral problem.
The conclusion that proceeds from the ensemble of the reflections presented in this paper could be the indication of the wisdom of an open ontology, which has not the pretension of knowing a priori how many ontological regions are in what is real, and which is ready to modify its framework according to the results of human research in its different sectors, without underestimating or overestimating anything. The systemstheoretic approach and the interdisciplinary attitude which today are imposing themselves more and more are already indications in this sense, and in this framework even reduction finds its place, to the extent that it exposes correlations, connections between diverse sectors and, by that, as we have observed, helps our understanding of complexity, without imposing the implicit metaphysicizations and the epistemological dogmatism of reductionism. After all, understanding difference while respecting its diversity helps us to better appreciate the marvellous variety and richness of what exists.
 See, for example, in this regard, BUNGE (1983), as well as BALZER, PEARCE, SCHMIDT, (1984).
 Not all reductionisms are of the type that we have just exemplified here and that is sometimes called a «downward» reductionism, since reduction proceeds toward a so to speak «inferior» level in the order of complexity. There are also examples of «upward» reductionism, as results when one reduces e.g. the explanations of all human behavior to the social structure (reduction of psychology to sociology). Finally, there are also so to speak directionless reductionisms, which limit themselves to reducing to a single fundamental core a sometimes very large variety of aspects of the real. For example, certain pretensions that have been advanced to reduce to psychoanalytic terms the understanding and explanation not only of psychic phenomena and individual behavior, but also of religion, art, and literature, of peace, war, politics and economics are forms of reductionism which are, so to speak, all-directional. This is why it appears appropriate to situate in the negation of the difference the specific feature of reductionism.
 For more details, we refer to AGAZZI (1969, 1978a, 1978b, 1980, 1988).
 For a more detailed exposition of the considerations elaborated here, one can see AGAZZI (1978c, 1979a, 1979b).
(1969): Temi e problemi di filosofia della fisica, Milano, Manfredi, 1969, Reprint Roma, Abete, 1974
(1978a): Les critères sémantiques pour la constitution de l'objet scientifique, in La sémantique dans les sciences (Colloque de l'Académie Internationale de Philosophie des Sciences:30 août-3septembre 1974, Rixensart), Bruxelles, Office International de Librairie, 1978, pp.13-29
(1978b): Eine Deutung der wissenschaftlichen Objektivität, in Allgemeine Zeitschrift für Philosophie, 3 (1978), pp.20-47
(1978c): L'objectivité scientifique est-elle possible sans la mesure?, in Diogène, 104 (1978), pp.96-115. Transl. in English: Is Scientific Objetivity Possible without Measurement?, in Diogenes, 104, pp.93-111
(1979a): Problèmes épistémologiques des sciences humaines, in Epistemologia, 2, special issue(1979), pp.39-66
(1979b): Analogicità del concetto di scienza. II problema del rigore e dell'oggettività nelle scienze umane, in AA.VV. Epistemologia e scienze umane, Milano, Massimo, 1979, pp.57-58
(1980): L'epistemologia contemporanea: il concetto attuale di scienza, in AA.VV. Scienza e filosofia oggi, Milano, Massimo, 1980, pp.7-20
(1988): L'objectivité scientifique, in E. Agazzi (ed.), L'objectivité dans les différentes sciences/Die Objektivität in den verschiedenen Wissenschaften, Editions Universitaires, Fribourg, 1988, pp.13-25
(1983): Understanding the World, Dordrecht-Boston, Reidel, 1983
BALZER, W. - PEARCE, D.A. - SCHMIDT, H.T.
(1984): Reduction in Science, Reidel, Dordrecht-Boston, 1984
E. Agazzi (ed.), The Problem of Reductionism in Science, Kluwer Academic Publishers, Dordrecht 1991, pp. 1-29.