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I try to understand the difference between holism and reductionism and I wonder whether the concept of emergence belongs to the first one or whether it is just "holism through the eyes of a reductionist".

As I understand, a holist is someone who thinks that systems should be considered as a whole, whereas a reductionist will try to reduce a system to its fundamental components to understand how the whole system works.

My question is the following : does a holist "believes" in the notion of emergence (from fundamental laws), or is emergence a concept coming from reductionism to explain complex system? In other words, can a holist accept the idea that a complex system behaviour is emerging from fundamental parts and their interaction or does it consider the whole system as indivisible (so the notion of emergence does not even exist)?

If emergence is a purely reductionist concept, then I think that holism if often misunderstood...


EDIT: To refine my question, let's take an example: the brain. Is the following true?

  • According to a reductionist, if you reduce the brain to its fundamental components (neurons/cells) you will be able to understand the whole brain. A possibility to understand the whole brain, would be to take a supercomputer, to simulate billions of neurons/cells, and the macroscopic properties of the whole will emerge through the computation. So brain = neurons+emergence.
  • According to a holistic approach, the brain can only be seen as the whole. It means that the brain is more than the sum of its parts and emergent properties. So if you simulate neurons/cells you will have emergent properties, but you will not find the behavior of the whole brain. So brain != neurons+emergence.
  • emergentism ? emergent properties ‘arise’ out of more fundamental entities and yet are ‘novel’ or ‘irreducible’ with respect to them – user6917 Jan 25 '15 at 5:47
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Emergence is the opposite of reduction. Holism is the opposite of separability.

The difference is subtle, but emergence and reduction are concerned with concepts, properties, types of phenomena, being deducible from other (lower level) ones, while holism is concerned with the behaviour of parts being independent from relational aspects, or their pertaining to a whole.

Following holism, the whole system should be considered, not only its parts and their interactions. A typical example is entanglement in quantum mechanics. That does not mean that new irreducible higher level concepts have to be used to address the whole system.

Following emergence, new properties appear at some level which cannot be deduced from the lower level and the arrangement of parts. This supposes some form of holism, since only the whole system has the property, yet the system could be separable with regards to its lower level properties. Typical (but controversial) examples could be biological and psychological concepts. One cannot necessarily say something is a gene from its molecular structure alone, because it could depend on the cellular context (respectively, a psychological character and a social context). Being a gene is emergent. Yet the gene could be separable into parts at the chemical level.

Also note that the concepts of emergence and reductionism are sometimes used loosely by scientists. Sometimes emergence refers to a higher level property which is actually reducible to the arrangement of lower level ones, and sometimes reductionism is implicitely used to refer to separability.

EDIT

In the brain example:

  • emergence would correspond to novel properties, typically psychological properties, or consciousness--you'd need specific concepts (psychological concepts) to address these new properties
  • reductionism would correspond to an expression of psychological properties in terms of neuronal properties (example: anger corresponds to such or such neuronal circuits being activated by such or such stimulus and producing such or such effect on the organism)
  • holism could be for example the fact that the electromagnetic field of the brain must be considered as a whole rather than the resultant of the electromagnetic field of separate neurons to correctly account for its evolution
  • separability would correspond to running a simulation of the electromagnetic field of the whole brain by assuming that it results from the electromagnetic field of separate neurons in a network, and obtaining empirically accurate results

In your question, what you call emergence is simply composition. Sometimes scientists use it as such, but philosophers usually mean irreducibility by emergence.

  • N.B. Entanglement can be understood mathematically by the composition of parts, as easily as randomness. It merely requires a correct approach to composing the parts. Which raises the question: is emergence in the eye of the composer — is reductionism always possible with a sufficiently clever notion of decomposition? – Niel de Beaudrap Jan 25 '15 at 19:00
  • I have added an example. If you could answer to the example, it would be great... – Vincent Jan 25 '15 at 19:11
  • I updated my answer – Quentin Ruyant Jan 25 '15 at 22:26
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An example of holism in physics is exhibited by what are called TQFTs; they are a 'toy' theories where toy means used for explorative and investigative work.

Think of one as a surface of some kind: a ball or a donut etc.

Then no Physically relevant information can be deduced about the theory by looking at it locally, ie in small patches of the surface; in fact all of the relevant information is contained in the global picture.

This then reduces by topological arguments to the number of holes in the surface.

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