In Special Sciences, Jerry Fodor talks about the unity of science via reductionism. Reductionism is the idea that mental phenomena can be reduced to/explained by physical phenomena. For example, being scared can be explained as the physical process of one’s heart rate increasing, or as a heightening of one’s awareness to his or her surroundings, or a series of neurons firing in a specific pattern, among other physical characteristics. To make this easier to follow, ‘an individual being scared’ will be represented as S1. Moreover, S1 can be explained as/is identical to the physical phenomenon of one’s heart rate increasing, which will be represented as P1, or a heightening of one’s awareness to his or her surroundings, which will be represented as P2, or neurons firing in a specific manner, which will be represented as P3. All of this can be represented in symbolic notation as: S1 = P1 v P2 v P3. Moreover, if an individual’s heart rate increases (P1), then physical law dictates his or her blood rate must also increase. An individual’s blood rate increasing will be represented as X. This can be represented in symbolic notation as P1 → X.
For illustration purposes, we will say S1 is a predicate of a law in special science, which states S1 → S2. In this hypothetical law, S1, as we already know, means ‘an individual is scared’. The other predicate, S2, we will say stands for ‘an individual screams’. So, to summarize, this law says, ‘if an individual is scared, then he or she will scream’. This can be represented in symbolic notation as S1 → S2. Furthermore, just as we know that S1 = P1 v P2 v P3, we can also reduce the predicate S2, thus explaining ‘an individual screams’ via a physical process. ‘An individual screams’ can be explained as/is identical to the physical phenomenon of certain chemicals firing in the brain, which will be represented as P*1, or as a vibration of the voice box, which will be represented as P*2, or as a sudden exhalation of air from the lungs, which will be represented as P*3, among many other physical processes. This can be represented in symbolic notation as: S2 = P*1 v P*2 v P*3.
Since S1 is identical to P1, or P2, or P3, and we know that if P1, then, by physical law, X, it has to follow that, if P1, which is identical with S1, then, by S1 → S2, the given individual is supposed to scream, but this will not occur. This is because there is a conflict between a physical law and a special science law. According to Fodor, when this type of conflict occurs, physical law always wins. Thus, when P1 occurs, which is identical to S1, X necessarily follows instead of S2, because X, which is not lawfully connected to any P*/S2 predicate, is the byproduct of a physical law, whereas S2 is the byproduct of a special science law. Furthermore, I have shown that S1 is identical to P1, or P2, or P3. So, if an individual’s heart rate increases, the conditions for P1 have been filled. Since P1 is identical to S1, the conditions for S1 have also been filled. Since the conditions for S1 have been filled, the conditions for S2 should also be met, but this is not the case, because the consequent X that follows from S1 takes priority over the consequent S2 that also follows from S1, because X is the consequent of a physical law, while S2 is the consequent of a special science law. As a result, a scenario arises where S1 occurs, but S2 does not follow, which is an exception to the hypothetical, special science law, S1 → S2. This is an example of how an exception to laws of special science can occur, which is what Fodor is talking about in Special Sciences.
You can read Fodor’s full article here.