Reductionism from a philosophical viewpoint

Question

Reductionism is the idea that knowledge at a higher level can be deduced from the entities and their interaction at a lower level. E.g. the claim that the properties of molecules can be deduced from the properties of atoms, the properties of cells can be deduced from the properties of molecules, . Do theories also have reductionist approach Theory T reduces to theory B when all of the truths of T (including the laws) have been translated into the language of B. Theory T reduces to theory B when all of the laws of T have been derived from those of B. Theory T reduces to theory B when all of the observations explained by T are also explained by B ?

Are theory reductionism and methodological reductionism same thing ?

Important point there are two different types of reductionism one is called methodological reductionism the other one Theory reductionism methodological reductionism is about the properties of the real world it's about taking things apart into smaller things and finding that the smaller things determine the behavior of the whole theory reductionism on the other hand means that you have levels of theories where the higher the emergent levels can be derived from the lower more fundamental levels but in this case a high level does not necessarily mean about large things and a low level does not necessarily mean it's about small things so what type of reductionism is it that has been so successful in the history of science the funny thing is that it's a combination of both methodological reductionism has so far gone hand-in-hand with theory reductionism as we have looked at smaller things we have found more fundamental theories but this does not necessarily have to remain this way there is no reason to think that the next better theory of nature will be found by studying shorter distances just because the two types of reductionism have been tied together for a while does not mean it will remain this way indeed some the biggest currently open problems in physics manifest themselves on large scales not on small scales besides dark energy and dark matter their source of the measurement problem in quantum mechanics they are not in any obvious way short distance phenomena so the next time a particle physicist tries to tell you that we need higher energies to probe shorter distances because that's where progress will come from remind them that methodological reductionism is not the same as Theory reductionism.

Answer 1

Reductionism is the idea that knowledge at a higher level can be deduced from the entities and their interaction at a lower level

there are multiple meanings to reductionism, and this is one of the stronger ones. There are weaker forms of reductionism. The way I like to phrase it is usually "ontological reductionism" vs "explanatory reductionism". An ontological reductionist need not commit to the idea that all higher level patterns are understandable in terms of lower level stuff, even if it's ontologically true that each instance of them is caused by lower level stuff happening.

Answer 2

The way I understand those terms, methodological reductionism is about a method ie an approach: it says that it might be a good idea to try and explain the functioning of a system or structure by looking at how elements of the system interact with one another. Nothing wrong about that.

Theoretical reductionism is another kettle of fish: it's about committing to a belief that small stuff always determines or explains fully the behavior of larger stuff. It's an exaggeration, in other words, a grand metaphysical claim with no particular utility, believed by folks who know very little about real science. A form of fetishism for the small stuff. Chemistry as we know it is not reduceable to physics, and biology does not reduce to chemistry. Each level requires its own concepts and laws.

Answer 3

Agreeing with your scetch of reductionism in science I want to illustrate the principle of reductionism by the some examples from physics and chemistry:

1. Theory T denotes thermodynamics. Typical physical quantities from T are pressure (P), temperature(t) and volume (V) of a certain quantity of an ideal gas. The main law is the state equation of the ideas gas

   P x V = n x R x t

   with n a measure of the quantity of gas contained in V and R a universal constant.

   Theory B is statistical mechanics applied to the corresponding set of gas molecules. The physical quantities of a single molecule within the given volume V are its kinetic energy (E) and its momentum (p; small letter). Taking the average for all molecules gives for the average energy of a molecule

   E_av ~ t

   and for the average squared momentum of a molecule

   (p^2)_av ~ P

   Statistical mechanics derives an equation between E_av and (p^2)_av, which reproduces the universal state equation from thermodynamics.

   For an introduction explaining the basic results from physics see the ideal-gas law.

   On the lower level of statistical mechanics the concepts of temperature and pressure of a molecule do not make any sense. On the higher level of thermodynamics the concept of the energy and momentum of a molecule make no sense. Hence both levels have their characteristic physical quantities which do not make sense on the other level.

2. More advanced is the reduction of the termodynamic concept of entropy to certain probability distributions on the level of statistical mechanics.

3. There are other examples of reductions, e.g., taking T the biological theory of information coding in genes, and B the chemistry of the composition of nucleid acids.

Answer 4

I agree with @Oliver5 that in science reductionism is more of an approach, than a philosophical viewpoint. In physics this is termed microscopic approach, as opposed to phenomenological theory, which describes phenomena as a whole, without delving into their microscopic mechanisms. Many basic physics laws are phenomenological - like Ohm's law, Hooke's law, Joule's law, etc.

Thermodynamics vs. statistical physics
A classical example is the dichotomy between thermodynamics and statistical physics. The former provides description of phenomena relating variables like pressure, temperature, volume, energy by postulating a series of thermodynamic laws. On the other hand, statistical physics considers objects as collections of atoms/molecules, and derives the same laws from some basic assumptions about how the large collection of particles would behave. Thus, in thermodynamics, entropy is postulated as a quantity that always increases - to account for the experimental observation that processes have preferential direction in time. On the other hand, microscopic theory defines entropy as a number of microstates, and explains the preferential direction of time in probabilistic terms. ( See Is information entropy the same as thermodynamic entropy? for various definitions of entropy.)

Emergence
There is also phenomenon called emergence, where the behavior of a large collection obeys laws that could not be predicted from the properties of its elementary constituents. Biological objects are a good example - humans clearly possess characteristics, that cannot be reduced to the properties of a single cell. But even one could cite simpler phenomena - like ferromagnetism or phase transitions of water (ice-liquid-gas), which are not reducible to the properties of separate molecules: see Does physics explain why the laws and behaviors observed in biology are as they are?

Answer 5

Non liquet, but to give one (pseudo)example of the failure of reductionism is intentionality in living organisms. Living things possess intentionality; so to reduce that to physics (for instance) would be to claim that even particles possess intentionality. Do they? Nescio.

A way out for the hard reductionist would be to adopt eliminative reductionism: Intentionality is an illusion/doesn't exist! I hear laughter, but I don't know who it is that laughs.