Especially for Paul, but probably interesting for other posters as well:
Ontological reduction is the theoretical reduction of one part of reality to what is naively conceived of as another part of reality.
In the case of the reduction of chemistry to physics, or of physiology to chemistry and physics, we see that the reduction really concerns the regularities of the processes taking place in the domain concerned. For example, chemical laws can be understood as special instances of physical laws and therefore chemistry can be reduced to physics. Similarly physiological laws can be understood as special instances of chemical and physical laws and therefore physiology can be reduced to chemistry and physics.
The reason why this type of reduction concerns laws rather than substance, is that the general underlying ontology states that the substance is one an the same in all of these cases, namely the physical world or matter. The generally assumed difference between biology and physics is not that one would be non-physical and the other physical, but that the first is clearly governed by more complex laws than the second.
The battle between reductionists and holists in this field concerns the question whether the laws governing biology can be reduced to physical laws or not. Holists claim that biological laws are radically different from physical laws rather than simply special, complex manifestations of them.
However, there is a second battle in theoretical biology, and that is the battle between reductionism and vitalism. Vitalism differs from holism in that it claims that biology is irreducible to physics, not primarily because of irreducible laws, but first of all because biology is about a different substance than physics, namely life (Latin: vita). Life would not just be a special manifestation of matter.
Similarly, in the philosophy of mind we find two battles which involve reductionism:
- Reductionism versus Holism. So far, there have been no proponents of holism in this thread. Holists, such as Roger Sperry, claim that the mind -though completely physical- functions according to special higher level laws which cannot be reduced to physiology.
- Reductionism versus Dualism. This is the battle of which I'm one of the main participants here.
(Idealism is a third position which is not so much a battle against reductionism but rather rejects the category of matter as irreducible to mind)
The question central to the reductionism vs. dualism debate concerning qualia is primarily one about substance, not about reducibility of the laws that govern the mind to physiology. In other words, we don't ask ourselves if consciousness can be said to function according to the laws we already know from physiology, but if consciousness IS really something different from the brain. So the causes of consciousness is not our primary concern, but the question whether consciousness can be regarded as a physical phenomenon. To answer this question it is not enough to state that mental laws can in principle be reduced to physiological laws. That would be begging the question, as you would just assume that the mind is nothing but the brain. Whereas the dualist position is that it is not, and that we have every reason to believe it is not and no reason to believe that it is.
I truly hope this helps.
Titus