In the past, I've worked on the idea that there are distinct levels in nature. It is often said that there are distinct realms in nature: the physical realm, the biological realm, the psychological realm, and the social realm for example. Each of these realms is supposed to have its own properties and laws. And the properties and laws of of a higher-level realm (psychology for example) supposedly cannot be reduced to those of a lower-level realm (physics for example).
It is of course undeniable that psychology (for example) needs to use its own concepts, over and above the concepts that physicists use. It would be absurd to take a psychological explanation of a psychological phenomenon and try to convert it into an explanation that only used the concepts that physicists use. In short, psychological explanations are not in practice reducible to physical explanations. Anti-reductionists go further than this, however. They think that this irreducibility-in-practice reflects a deeper truth about the world, rather than merely reflecting our cognitive limitations. They claim that:
  1. Explanations invoking psychological concepts cannot be replaced by explanations invoking physical concepts, not even even in principle.
  2. Psychological laws are not physical laws.
  3. Psychological kinds / properties exist.
  4. Psychological kinds are objective natural kinds.
  5. Psychological properties are distinct from physical properties.
 
I'm not convinced by 1 2 4 and 5 above.
For a start, I think that the reductionist vs antireductionist debate is set up in a way that is filled with unhelpful ambiguities. The first contribution I hope to have made is in Paper 4, in which I try to clarify the anti-reductionist's claim that higher-level explanations abstract away from the messy details of lower-level explanations and thus provide some additional understanding that lower-level explanations do not provide. There are four different ways in which higher-level explanation might be said to do this, I show, and various competing reasons to think that doing this is an explanatory virtue.
The second contribution I hope to have made is in Paper 5, in which I clarify various distinct ways in which one explanation can be said to be on a higher level than another explanation. I also argue that the only interesting way of interpreting the debate over "in principle replaceability" of explanations is as a debate over whether higher-level patterns constitute genuine laws and over whether higher-level properties constitute objective natural kinds.
Having engaged in this clarificatory work, focusing on higher level versus lower level concepts and explanations, I then turn my focus to higher level versus lower level properties. In Paper 6, I argue there is no interesting sense in which higher-level properties are distinct from lower-level properties, unless you are willing to make causal inference a complete mystery, or unless you are willing to make property individuation a complete mystery. (Qualification: so long as higher-level facts supervene upon lower-level facts.)