When someone puts forward an argument that sounds clear and logical, you may occasionally hear it dismissed with the words, "that is just reductionist." The word reductionist is used in such cases to imply that the argument is unduly simplified or distorts the issue. Reductionist thinking, it is implied, leaves out something essential, a romantic or spiritual element.

Reduction is an integral part of scientific thinking. Because of this, some people think that science, and biological science in particular, is invalid or unreliable. They might describe science as atheistic, deterministic, or simplistic.

This essay discusses the concept of reductionism, its inherent limitations, and its often misunderstood counterpart, the phenomenon of emergence.

Reduction is an analytical process, identifying the parts of something and examining their relationships to each other and to the whole. The operation of a motor car, for example, could be explained by describing the operation and interaction of the engine, the transmission, the steering etc. Or, to give a scientific example, a molecule of water is commonly symbolised as H2O, which means that it is composed of two atoms of hydrogen and one atom of oxygen which have interacted to produce a new entity. The characteristics of hydrogen and oxygen atoms are used to explain how they unite and how the water molecule behaves as a distinct unit. Similar explanations apply for all chemical compounds. This may be expressed as "the whole is the sum of its parts", with the process of reduction being expressed as "reducing the whole to its parts".

So a reductionist argument is that chemistry can be explained purely in terms of the physics of atoms. And the argument goes further. Biochemistry can be explained by chemistry. The operation of the cells of living organisms can be explained by their structure and their biochemistry, and similarly for the physiology of organisms themselves in terms of their parts. And the physiology explains the behaviour of the individual organisms, which explains how individuals operate as societies.

This suggests that the workings of society could be explained using nothing but physics, which very few people would take seriously, and that mathematics and physics are somehow "more true", or at least more reliable, than the biological sciences. Some scientists, or at least those associated with the physical sciences, feel this may be true. But the formulas and the usually unseen atoms, molecules, etc., of the physical sciences are not obviously real to most people in the way that visible objects and organisms of the everyday world are. Some people regard human consciousness to be more real than any part of science.

This description of reductionism is crude, but it is not far removed from the general impression of what reductionism is, and it gives a hint as to why some people dislike it. Before exploring the issues further it would be helpful to first look at some aspects of science.

Some Aspects of Science

Science is sometimes characterised as a combination of "stamp-collecting" and "storytelling". The stamp-collecting consists of gathering and examining pieces of information about the world, and then classifying the pieces into groups according to their apparent relationships or common characteristics. The storytelling then explains how the similarities and the differences might have occurred and how everything works together. And, of course, the storytelling is what is called scientific theory.

Science starts with the observable. When observed phenomena are analysed, ie., reduced to their parts, theories are devised to explain how the parts "produce" the phenomena. So in closely looking at things, as distinct from happening to notice them, and in noting characteristics, reduction is part of observation. It is also part of creating theories.

Usually, with a large set of parts, as in a Lego set or in nature, it is possible to build many different things. With a Lego set you might build a bridge or a tower, etc. A group of amino acids can be built up into a huge range of different types of proteins. However, to be able to predict precisely what will be built on a particular occasion, there needs to be either very few parts, or parts with specifically identifiable functions. That is, unless with the Lego set the instruction book is open at the right page, or with the amino acids you know the particular gene sequence that is assembling them. So, while chemistry can be explained using physics, physicists could not have discovered much about chemistry without already knowing about chemical phenomena. That is one reason why sociology cannot be derived from the physics of atoms and electrons.

In contrast, no matter how many times something is correctly analysed, the same set of parts will always be found. So at each stage of complexity it should be possible to analyse something to find how the parts explain the whole.

The value of any analytical process, including "reassembling" the parts to provide an explanation, depends on the accuracy and completeness of the descriptions of everything in the analysis and on the validity of the reasoning employed. The process often leads to new information being discovered about either the parts or the whole or both. Over time, scientific theories are modified or superseded, as new discoveries are made or new theories are devised.

Sometimes no theory about a particular phenomenon can be devised that is completely consistent with the rest of science. More than one explanation may closely fit the evidence, each with different shortcomings. Then the theory that seems to be the best fit has to be tentatively accepted. Deciding which theory is the better fit is a continuing cause of controversy within science, which can only be resolved by re-examining previous findings, making new discoveries, or developing a better theory.


There is a great deal of difference between an assembled car and all its parts laid out ready to be assembled. Without any prior knowledge about cars, and if the parts were in the form of the unassembled basic components – nuts, bolts and all the other bits - it would be virtually impossible to know how put the car together properly, particularly if there were more of some of the parts than needed.

Turning from technology to nature, we experience water as a fairly heavy liquid. Liquid water consists of trillions of H2O molecules in constant motion and continually interacting with each other. It can be very surprising when one first learns that the formation and characteristics of water vapour, of liquid water, and of water assembled into ice or snowflakes can be explained in terms of the atoms of hydrogen and oxygen, which are gases, one of which we are constantly breathing, and so unlike water.

In fact, it looks as if water is more than just the sum of its parts. The complete motor car, assembled with knowledge and skill, is more than the sum of its parts. The difference is the applied knowledge, skill and effort, and the use of appropriate tools. Is reductionism blind to this fact? At every level of complexity, people will point to the differences between the whole and its parts, and ask where the new characteristics came from.

One answer is that they were provided by some entity outside the material world, something spiritual or supernatural. This can be a comforting answer, because reductionism implies a mechanical determinism, which may feel OK for basic physical and chemical processes, but uncomfortable when reductionism is applied to living things, including us. Also, it seems reasonable. In Nature there is no noticeable assembly plant with a staff of experts, so there must be an unseen skilled agency.

There is indeed an agency, and it pervades the natural world. Nature’s parts assemble themselves, unlike those of manufactured goods. The parts in a car do not spontaneously interact with each other to produce a connected system. And there are not many different ways – other than swapping one wheel for another, etc. - in which they can be usefully assembled. But electrons, protons, etc., intrinsically interact, and they connect in ways that can become extremely complex as the assembly grows in size. Also, the number of possible arrangements increases enormously as the number of components increases. Each particular arrangement is merely one of a myriad possibilities, each with its own characteristics – its solidity or fragility, its reactivity or inertness, etc.

So, even in the unplanned processes of Nature, one might start with an assembly, examine its parts and find out how it works, but not be able to predict all the possible ways the parts (all or some of them) could be assembled, or how the assemblies would behave. Further, it is possible for apparently haphazard processes to make very complex assemblies. This needs only repeated and varying action, and often plenty of time.

To illustrate these points, think of very flexible sticks with fishhooks at their ends. One in isolation may seem very simple, but toss a pile of them into a bucket and shake them vigorously and one or more tangled masses will be produced. Throw several such tangles onto a pool of water in which there are a lot of fluffy tennis balls and stir them around. Repeat the experiment several times with products of each round being added to the next. Small rafts would probably be produced, with size and shape depending on the number of balls and the sizes of the tangles of sticks. It is likely that some of the results would be rafts that could support one or more people, but it would be hard to predict their exact shape.

If the sticks and balls were strongly interactive and there was a larger range of interacting things, and the conditions of mixing were different every time the experiment was tried, then it would become very difficult to predict what would be formed. But it would be difficult to argue that the whole conglomeration was more than the sum of the parts.

Nature is much more complex than this example. It is more diverse in type and more reactive in many ways. Combinations can be produced where conditions become "non-linear", that is, small changes can produce effects that are disproportionately large, and vice versa. Without knowing the precise conditions it becomes impossible to predict the outcome: but once there is an outcome, it can be analysed into its component parts, with the processes of its assembly explained. The outcome may, and generally does, have properties that seem to be greater than the sum of the parts. These are emergent properties. And this applies not only to inanimate material but also to living tissue and organisms.

When looked at individually, most items of any kind display only a part of their characteristics. But when they interact with other items as parts of something larger, additional characteristics are revealed. An atom of hydrogen by itself is just a proton and an electron held in partnership by electrical attraction and sub-atomic forces. When brought close to another atom it is seen to be chemically active. Its reaction with certain types of molecules produces an acid, and when the acid contacts water the hydrogen atom dissociates from the main body of the acid, leaving its electron behind and becoming a positively charged hydrogen ion, which then loosely associates with a molecule of water.

A virus by itself is just a deeply textured bag made of protein and containing some genetic material. But when it comes in contact with a living cell whose coating has a texture that it can latch on to - like the two textures of velcro – the virus can pour its genetic material into the cell and cause the cell to assemble copies of the virus. If the cell is already infected with a virus, some of the genetic material might be exchanged between the two viruses, resulting in new strains.

And human beings in isolation do not reveal the characteristics that determine their behaviour when interacting with one other person, or in a small group, or in a mob.

So unexpected inherent characteristics may emerge when things interact with various parts of their environment. These "hidden" characteristics must be included whenever parts are added to equal the whole, and they account for the emergent properties of the whole.

When I was first introduced to chemistry I marvelled at the destructive rage of the pure elements sodium and chlorine, and that their tempestuous union produced the comparatively benign result of sodium chloride, which is common salt. Shortly afterward I learnt that this was the (emergent) result of their great urge to shed or gain an electron, and later that, according to quantum theory, this urge was the result of the numbers 11 and 17, which are the numbers of electrons in the shells of their uncharged atoms.

All of the properties of salt emerge from the characteristics of sodium and chlorine. These include how it dissociates when dissolved in water, which is different from what happens when sugar, for example, dissolves in water. They also include such things as the role of salt in living organisms, including how it regulates the speed of heartbeats. These can be completely explained in a way that is reductionist.

But is reduction sufficient to show how every aspect of every kind of observed phenomenon occurs? Some people think that reductionism becomes unreliable when things get more and more complex (and often more poorly understood) as in the workings of brains or ecosystems, or in social interactions, or in quantum theory. If such things can be regarded as systems of interacting members, a reductionist analysis should be possible, but it can go only as far as the available information and analytical skill allow. Further resolution might then be found by research.

Actually, it is never possible to know whether everything has been discovered about anything. While this does not mean that there must necessarily be some external non-material entity whenever there is an unexplained detail, some people hope it might. So whether an explanation is sufficiently complete could be one of opinion – or is it just one of emotion?

It might be possible to answer this question by looking at some assumptions that underlie science. Two principles that are intrinsic to scientific reasoning are causality and consistency. Causality means that everything that happens is the result of some process. Consistency means that each type of process always operates in the same way. It is these that lead to the principle that all scientific theories must be compatible. Reductionism, as a part of scientific reasoning, complies with these principles.

If one or both of these principles were untrue, might an emergent characteristic be attributable to the action of some non-material entity? It might be argued that these principles appear to be true only because some non-material entity makes them appear so. For such an entity to be credible, its characteristics would need to be described and validated. In any case, invoking such a "helpful" entity would not affect the status of science as a reliable explanation or as a foundation for research and invention.

There is also the issue of whether there are truly random phenomena that break the rules of causality and consistency, allowing for such things as free will. If this actually happens, then there should be evidence of anomalous phenomena or things that science cannot explain.

Examples of observed phenomena that appear anomalous and inexplicable are the expansion of the universe, how spinning galaxies avoid flying apart, and many down-to-earth phenomena such as superconductivity. These all occur consistently so are not random. Scientists regard them as mysteries to be solved scientifically, and propose new scientific theories to account for them. There are other cases, such as the explanation of consciousness, that some people attribute to some supernatural entity but that others think can be explained scientifically as emergent properties of matter.

If any unknown entity, either natural or supernatural, is proposed in order to account for an otherwise unexplained emergent property, then some description of that entity is needed. To be credible, the description should include how the entity might produce the emergent property, and be capable of being tested.


So, does reductionism make science essentially deterministic, atheistic and narrow-minded? Does it make science simplistic or unreliable?

If every theory in science is logically consistent with every other, if the idea of consistent cause and effect is true, and if logic is entirely valid, then science must be entirely deterministic. That does not mean that everything in the future could then be predicted. To do that would require knowledge of everything about the present, which is intrinsically impossible. Even then, chaos theory would require absolute precision and quantum uncertainty blurs precision. Reductionism does imply that the whole world is just a very complex machine running within clearly defined limits.

The unity of science leads to the view that everything is an interconnected whole. Since science deals only with the natural, ie., observable, world, the supernatural is, by definition, excluded from it. This implies that whatever can be observed, measured and analysed, and which behaves consistently, must implicitly be material not supernatural. Consequently, reductionism, as a part of science, excludes the supernatural. Acceptance of science as the current explanation that best fits what is observed about the world does not necessarily imply atheism. That depends on how you define atheism, and on your view of what relationship a non-material agency might have with the material world. People who believe there exists a non-material entity (which includes some scientists) may think that science is narrow-minded - although they might also agree with its findings.

Reduction would make science narrow-minded if it opposed "looking at the bigger picture". But it doesn’t. Anyone who is analysing a situation, scientific or otherwise, can choose any starting point among all conceivable levels of complexity.

Science rests on the validity and completeness of its observations, which are continually published and checked, and on the validity of its logic, which is continually examined and argued. Despite the care with which science has been put together, there is always the possibility that observations it rests on have been misinterpreted, or that phenomena yet to be observed will contradict present theories, or that the reasoning that explains the observations contains unnoticed incorrect assumptions. This does not mean that any particular part of science must be wrong. Most of it matches very closely the world as we see it. Scientists continually strive to widen its perspective, modify its theories accordingly, and refine its accuracy.

Science is rigorous and very complex. Reductionism, as one of its key tools, by no means makes it simplistic.


This is the text or the talk given to the Atheist Society, Melbourne
on 14 April 2009 by Graeme Lindenmayer
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