One of the most prevalent ideas in modern philosophy of science is the idea of the unity of science as articulated by Oppenheim and Putnam. The claims made by these two philosophers roughly states that every explanation in a science can be derived from a general law in that science, and that the laws of all the sciences can be reduced to physical laws. Thus, on the premise of physicalism, this hypothesis claims that all law of the higher level sciences (sociology, economics) can be reduced to the laws of physics. This claim means that bridge laws are actually identity statements. Bridge laws are statements that state a relationship between a law from one science with a law from another; they bridge the laws of one science to another, but there are other concievable possibilities besides identity, which include causation or correlation. Thus, the description that one has a certain mental state like anger is the same as a physical statement about the state of the matter of the brain; this needs to be distinguished from the claim that the physical state of the matter of the brain as something that causes anger. Thus, implicitly one has to accept the traditional materialist position in philosophy of mind, in order to accept the unity of science hyepothesis put forth by Putnam and Oppenheim. One cannot hold that the mind and consciousness are emergent while retaining a belief in the possibility of reducing all scientific statements to statements of the laws of physics.
The unity of science hypothesis makes a very strong claim, but in many sense it is appealing, in that it provides a way of explaining the world in purely physical terms and allows one to speak about mental states without them being illusory in anyway; however, the claim that is made by this thesis is deeply flawed.
The first problem with the thesis that I have been discussing is the problem of Multiple Realizability. This problem simply states that qualities are realizable in more than one physical way, and thus bridge laws are often not statements of identity, but rather can be seen as statements of correlation or causation. One example, Fodor gives is the idea of a currency, there is nothing inherent in the physical structure of a currency that makes it a currency, the quality of being a currency can be realized in more than one physical way, through gold, silver or fiat notes. Fodor's argument cannot be taken as a conceptual refutation of the reductionism supposed by Putnam and Oppenheim, but rather a piece of empirical conjecture, because there is a way around his currency example on a conceptual level. One could say that what makes a currency a currency is not the state of the physical object that is viewed as a currency, but the attitudes which are reducible to physical states towards the physical thing, which qualify it as currency. Given that Putnam and Oppenheim's is an empirical hypothesis Fodor's example does not refute the thesis. Their hypothesis is still conceptually possible; however, its tenability is reduced whenever a situation arises in which the reduction claim they are trying to make becomes quite difficult to make.
The last thing and the major reason I had for writing this blog was to discuss the idea of teological explanation as a reason to reject the reductive physicalism that is implied by Oppenheim and Putnam, over and above the comments of people like Fodor. The use of teleological explanation is exceedingly common in Biology, Sociology and Economics and for simplicity's sake I will discuss Biology as it has the strongest claim as a true science to those who endorse the scientism that often goes along with reductive physicalism. When a Biologist says that the function of the eye is to see, he is making a very clear claim about the status of the eye that cannot be reduced to an exposition in the terms of particle physics, in this sense an expression in particle physics cannot express the meaning and content of statements that invoke the concept of function. It is true that teleological statements do necessarily presuppose that there is an end for living creatures, and that is survival. A reductive physicalist could say that the survival instinct is reducible to a part of the brain, which is hence reducible to the laws of physics, but there would be a loss in the content of the statement that would occur through this reduction. Stating that an animal has an instinct to survive, is quite different from saying that its function is to survive, in the same sense that saying that the eyes are for seeing is different from saying that the eyes see. What is revealed by this difficulty is a distinction between whether physical structure is dominant or matter is dominant. It may be quite obvious by now that I take the position that the former is dominant, and the latter is not; however, I will not go any further on this topic, than to say that it seems to make more sense to try to understand things and phenomena in terms of their overarching structure rather than the stuff they are made of. If I want to understand a table, I do not look to the fact that it is made of wood, otherwise I could understand a table by understanding an Oak Tree. I look to the overarching structure of the thing that I wish to understand.