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 I. Types of reductionism - II. Hierarchy and emergence - III. Insights from science - IV. Philosophical and theological aspects of reductionism. 1. Rationality. 2. Metaphysics. 3. Theological issues. - V. Concluding remarks. 1. Levels of description. 2. One world.

A reductionist believes that a complex system is nothing but the sum of its parts. An account of it can be reduced to accounts of individual constituents. An antireductionist believes that the whole is more than the sum of its parts. There are holistic properties that cannot be described in purely constituent terms.

I. Types of Reductionism

Constituent reductionism accepts that when a complex system is actually decomposed, the resulting fragments will just be those corresponding to the expected constituents. For example, a living organism can be split up into its component molecules and there will not be any extra ingredient left over, such as the spark of life that vitalism claimed distinguished living entities from inanimate matter. This type of reductionism is very widely accepted. It by no means implies, however, that living beings are “nothing but” collections of molecules, for the decomposition will have brought about the death of the organism. Reductionism of this kind is closely related to methodological reductionism, the widely practised scientific strategy of studying wholes through breaking them up into their constituent parts. Again, the success of the strategy does not imply that everything relevant to the whole can be studied in this way.

A second type of reductionism may be called conceptual reductionism, in which it is claimed that the concepts applicable to the whole can be totally expressed in terms of concepts applying to the parts. The term epistemological reductionism is also used for this type. An example of a successful reduction of this kind is afforded by the use of the kinetic theory of gases to reduce the concept of temperature (originating in the thermodynamics of bulk matter) to exact equivalence to the average kinetic energy of the molecules of the gas. However, there are many examples that suggest that reductions of this kind cannot always be made. Individual water molecules do not possess the property of wetness, which is a conceptually irreducible aspect of the behaviour of large collections of such molecules (generated by the inter-molecular forces that are the source of the bulk property called surface tension). Biological science makes use of many essential concepts, such as fitness, adaptation, organ, sexuality, ecological niche, which cannot be translated into statements about molecules.

A third type is causal reductionism, which implies that the causes acting on the whole are simply the sum of the effects of the individual causalities of the parts. In the case of wetness such a reduction appears successful, on the reasonable supposition that surface tension is generated entirely by the action of inter-molecular forces. Since at both levels one is concerned with purely energetic properties, a translation between the two seems plausible. On the other hand, it is not at all clear that sums of firings of neural synapses can add up to produce mental qualia (feels), as there appears to be a clear qualitative difference between the two. Causal reductionism is closely allied to ontological reductionism, the assertion that the whole is the sum of its parts. It is quite possible to hold to constituent reductionism and to deny causal reductionism as, in fact, many do. One strategy for this is to embrace contextualism, the belief that the behaviour of constituents depends upon the nature of the whole that they constitute.

II. Hierarchy and Emergence

If all three types of reduction hold, a position one might call strong reductionism, then the truly basic ontology is exclusively that of the fundamental constituents. All the rest is mere elaboration. From such a point of view, elementary particle physics is the foundational discipline, and everything else, including the rest of physics, through biology and on to psychology, anthropology and sociology, would be just a collection of corollaries. This would constitute the modern equivalent of the ancient assertion that all is “atoms and the void” ( MATERIALISM, I). Of course, such a claim could only be made in principle, as the drawing of these corollaries would be very far beyond human capacity. Even in physics, the totally adequate description of a macroscopic lump of matter would involve discussing the behaviour of a collection of atoms of the order of 1023 in number. In other words, reductionist or antireductionist claims are always metaphysical in character. They may be motivated by extrapolations from results in the natural and the human sciences, but they can never be fully substantiated by scientific arguments alone.

In practical terms, therefore, there is a hierarchy of the sciences, in which the “higher”draws upon the resources of the “lower”, but it needs also to make use of its own style of argument and conceptual apparatus in addressing the problems posed by its own particular phenomena. Chemistry is related to physics in this way, and biology is similarly related to both of them. Above biology, lies the succession of the human sciences: psychology, anthropology, sociology. The hierarchy is ordered in a natural way that depends upon some concept of increasing complexity. Although there are technical difficulties in the precise definition of the meaning of increase in complexity, it is intuitively persuasive that the sequence: quark, molecule, cell, multicellular entity, conscious being, self-conscious being, represents an ascending scale of this kind. It is important to recognise that it is not merely size that is the essence of complexity, but the degree of intrinsic inter-relationship and mutuality present between the parts. Although the observable universe contains 1022 stars, cosmology is a great deal simpler subject than human biology.

The levels of a hierarchy can be distinguished by the emergence at a higher level of properties that are not manifested at lower levels. Life and consciousness are the two most striking instances of emergence that are known to us. A critical question is whether the phenomenon of emergence is simply the expression of conceptual antireductionism, or whether it is of deeper ontological significance. We have seen that the emergence of the wetness of water seems to be simply an example of the conceptual kind, in which energetic properties at one level produce energetic properties at the higher level in an unproblematic way. On the other hand, the emergence of consciousness appears to be one that resists understanding in purely conceptually emergent terms. A big gap yawns between methodologically reductive accounts of neural processes and the simplest conscious mental experiences, such as feeling hungry or seeing blue, with no obvious bridge between the two. This recognition raises the question of whether there may not also be causal antireductionism involved in this case. If the execution of mental intentions is a free act of the human person, this would then seem to the case, for an irreducibly holistic causality (human intention) would be acting.

Finally, we may note that people of a strongly reductionist tendency, such as Francis Crick (1994) and Richard Dawkins (1976), do not go below the level of their own discipline for explanatory purposes, but are content to frame their accounts in terms of molecules or genes, without pressing on to the quark level.


III. Insights from Science

It is useful to note a number of indications from modern science that encourage adopting an antireductionist stance:

a) Contrary to the Newtonian picture of a physics concerned with atoms moving in the void of a spatial container ( MECHANICS, III.1), Einstein`s general  relativity ties together space, time and matter in intrinsic inter-relationship.

b) The EPR effect [Einstein, Podolski, Rosen] shows that once two quantum entities have interacted with each other, they remain mutually entangled, however far they separate, so that effectively they remain a single system ( QUANTUM MECHANICS, V). The subatomic world cannot properly be described in atomistic terms.

c) Complex physical systems display many properties that could not have been foreseen from consideration of their constituents on their own. For example, electrons moving in metals have a band structure for their energy levels. This means that there are some ranges of energy that are accessible to them and some which are not. This is in complete contrast to the behaviour of individual free electrons, whose energies can take any value.

d) Chaos theory (cf. Gleick 1988) is the study of systems that are exquisitely sensitive to the finest detail of their circumstances, so that the slightest change in their surroundings totally changes their future behaviour. Such systems are widespread and their environmental vulnerability means that they are not truly isolatable. They must, therefore, be considered holistically, in their total context.

e) Complexity theory (cf. Kauffman 1995) is concerned with the behaviour of complex systems (see above, c) whose constituents are inter-related in some specific way. At present in its infancy and largely based on computer modelling, this new science has shown that systems of this kind are capable of spontaneously generating astonishing degrees of overall pattern in their behaviour. This has suggested to some that when a proper formulation of the theory is found, it will involve not only exchanges between constituents but also a kind of holistic pattern-forming capability which has been dubbed “active information” (cf. Polkinghorne 1998a).

f) Biological cells are biochemical systems of great inter-related complexity. Although it has become conventional to talk of DNA as carrying information ( BIOLOGY, IV), this informational content is only meaningful and activated within the total context of the living cell. In isolation, DNA is no more than a very complex chemical.

g) The Nobel prize-winning brain scientist, Roger Sperry (cf. Sperry, 1983), introduced the concept of “top-down causality”, the influence of the whole upon its parts which he believed was involved in the causal transactions taking place between mind and brain. The idea of top-down causation has subsequently been taken up by a number of other writers.

IV. Philosophical and theological aspects of reductionism

1. Rationality. Strong reductionism faces a problem in relation to the nature of rationality. If reality is no more than the interactions of elementary particles, then everything just happens and who is to say that the mouthings of human automata are the articulations of rational discourse? What could authenticate that utterance as being valid and truthful? The strong reductionist saws off the very branch on which he seeks to sit, by putting in jeopardy the arguments believed to defend his position.

2. Metaphysics. The classical philosophical positions of physicalism or idealism are both essentially reductionist in character, as they reduce reality simply to the material or to the mental. Substance dualism, of a Platonic or Cartesian kind, is essentially antireductionist in the sense of allowing reality both to the material and to the mental. However, it has encountered many problems, rooted in its difficulty in explaining how the mental and the material relate to each other. There are a number of other contemporary philosophical positions that are also antireductionist in character.

One is dual-aspect monism (sometimes also called non-reductive physicalism) which asserts that there is only one kind of substance but that it can be experienced the two complementary poles of the material and the mental. Such an even-handed treatment of mind/matter is antireductionist. In a different way, A.N.Whitehead`s (1861-1947) process thought also resists reductionism. It is based on a metaphysics of individual events (“actual occasions”). These can be of varying degrees of complexity and they are not to be reduced to a single common denominator. Another antireductionist proposal was made by Niels Bohr (1885-1962) when he suggested exporting from quantum mechanics his concept of complementarity and using it as a way of relating life and matter. Bohr emphasised the point, already noted, that reducing a living entity to its molecular parts serves to kill it, so that encountering it in its holistic integrity or in its material decomposition are mutually incompatible alternatives. None of these metaphysical formulations, however, are without their difficulties.

3. Theological Issues. It is scarcely necessary to emphasise the interest of theology in an antireductionist understanding of reality. From Lucretius (98-54 B.C.) onwards, those who have supposed that there is nothing but atoms and the void have also espoused  atheism. The reality of the mental and the spiritual is vital to religion, and the reality of the material is vital to Christianity, the religion of the Word made flesh ( JESUS CHRIST, INCARNATION AND DOCTRINE OF LOGOS, IV). Theology should take heart from the fact that there is sufficient encouragement, both from science properly construed and from philosophy carefully pursued, to defend the antireductionist position.


V. Concluding remarks

1. Levels of description. The knowledge we obtain from our exploration of the world (we report here what already written elsewhere, cf. Polkinghorne, 1987, pp. 86-87 and pp. 97-98), can be organized into a hierarchy, corresponding to the complexity of the systems treated as basic: physics, chemistry, biochemistry, biology, psychology, sociology, theology. The question is how these different levels of description relate to each other. The thorough-going reductionist offers us an answer: ultimately all is physics ( POSITIVISM). Everything else is nothing but an epiphenomenal ripple on the surface of a physical substrate, just as waves generated by the wind in a field of corn are nothing but the motions of many ears of wheat. It is an answer of great simplicity and implausibility. I a Rembrandt self-portrait nothing but a collection of specks of paint? A Shakespearean sonnet nothing but a pattern of ink marks on a sheet paper? If we take the picture or the printed poem apart that is all we shall find. There will not be an extra ingredient, the spirit of art or poetry, to be found in the residue. It seems to me that we can accept a structural reductionism, that the units out of which all the entities of the physical world are constructed are just the elementary particles studied by fundamental physics. In biology vitalism seems justly dead. The successes of molecular biology do not encourage us to believe that a mysterious entelechy or élan vital is an additive necessary to turn inanimate matter into living being. It is an entirely different proposition to add to this , as our thorough-going reductionist does, a conceptual reductionism which denies the emergence, with increasing complexity of organization, of totally new levels of meaning and possibility which are not in principle reducible to those which lie below them. If structural reductionism is not to lead to conceptual reductionism a careful investigation is necessary into the extent to which genuine novelty can come into being with these increasing degrees of organization. To what extent is the whole more than the sum of its parts? It must surely be through the enhancing effect of mutual co-operative interaction, made possible by integrating components into a larger unity.

I believe that those who defend the  autonomy of their subject against the imperialist claims of physics are right to do so. Animals are made of atoms but that does not imply that biology is just a complicate corollary to atomic physics. Characteristically, biological concepts need for their understanding the total living setting in which they find their expression. Consider a sentence like: «molecular biology has given us considerable biochemical insight into how the genetic blueprint is encoded onto DNA and how messenger RNA transfers appropriate parts of that plan to control the production of proteins». It speaks a hopelessly mixed language. Biochemistry can talk about the molecular dynamics of aggregating amino acids to form proteins. The information-carrying language of “blueprint” and “plan” refers to a different and disjoint type of discourse which only begins to make sense in a cellular context.

2. One world. It was said, perhaps unjustly, of the great 19th century experimental physicist Michael Faraday, who was a committed Christian believer, that when he went into his laboratory he forgot his religion and when he came out again he forgot his science. I hope that it is not true. We live in one world and science and  theology explore different aspects of it. The burden of our tale has been that, despite the obvious differences of subject matters, the two disciplines have in common the fact that they both involve corrigible attempts to understand  experience. They are both concerned with exploring , and submitting to, the way things are. Because of this they are capable of interacting with each other: theology explaining the source of the rational order and structure which science both assumes and confirms in its investigations of the world; science by its study of creation setting conditions of consonance which must be satisfied by any account of the Creator and his activity. The relationship is not free from puzzles but I have sought to show that no act of mental compartmentalism or dishonest adjustment is required of those who take with equal seriousness the stories told by science and by faith.

Reality is a multi-layered unity. I can perceive another person as an aggregation of atoms, an open biochemical system in interaction with the environment, a specimen of homo sapiens, an object of beauty, someone whose needs deserve my respect and compassion, a brother for whom Christ died. All are true and all mysteriously coinhere in that one person. To deny one of these levels is to diminish both that person and myself, the perceiver; to do less than justice to the richness of reality. part of the case for theism is that in God the Creator, the ground of all that is, these different levels find their lodging and their guarantee. He is the source of connection, the one whose creative act holds in one the world-views of science, aesthetics, ethics and religion, as expression of his reason, joy, will and presence.

This interlocking character of the world of creation finds its fullest expression in the concept of sacrament, an outward and visible sign of an inward and spiritual grace, a wonderful fusion of the concerns of science and theology. Thus in the Eucharistic bread and wine which, in the words of liturgy, «earth has given and human hands have made», become the body and the blood of Christ, the source of spiritual life. The greatest sacrament, compared to which all the others are types and shadows, is the Incarnation in which «the Word became flesh and dwelt among us, full of grace and truth; we have beheld his glory, glory as of the only Son from the Father» (Jn 1,14). The Word, the Lógos, combines two notions, one Greek, one Hebrew. For the Greek the lógos was the rational ordering principle of the universe. For the Hebrew the word of the Lord was God’s activity in the world. Science discerns a world of rational order developing through the unfolding of process, a fusion of Greek and Hebrew insights. Theology declares that world in its scientific character to be an expression of the Word of God. For «all things were made through him, and without him was not anything made that was made» (Jn 1,3).

Documents of the Catholic Church related to the subject: 

R. DAWKINS, The Selfish Gene, Oxford Univ. Press, Oxford 1976; R.W. SPERRY, Science and Moral Priority, Columbia Univ. Press, New York 1983; A.R. PEACOCKE, God and the New Biology, Dent, London 1986, chs. 1-4; J. POLKINGHORNE, One World. The Interaction of Science and Theology, Princeton Univ. Press, Princeton (NJ) 1987; J. GLEICK, Chaos, Heinneman, London 1988; I.G. BARBOUR, Religion in an Age of Science, Harper and Row, New York 1990, pp. 165-171; E. Agazzi (ed.), The Problem of Reductionism in Science, Kluwer, Dordrecht 1991; F.H.C. CRICK, The Astonishing Hypothesis, Simon and Schuster, London 1994; S. KAUFFMAN, At Home in the Universe, Oxford Univ. Press, New York 1995; J.C. POLKINGHORNE, Belief in God in an Age of Science, Yale Univ. Press, New Haven 1998, ch. 3; J.C. POLKINGHORNE, Science and Theology, SPCK, London 1998, pp. 50-62.