Eric Olson’s main contention is that when we refer to “I” we should be referring to one thing or perhaps no thing, but not multiple things. For any theory of identity one must avoid the thinking animal problem – positing more than one entity answering to the reference “I.”
Olsen’s suggestion is that we are animals. Animalism is the view that each human being is numerically identical with an animal. An animal is a biological organism that lives by virtue of being a self-organizing “biological event” that maintains a complex internal structure.
According to Olson, common theories fail to avoid falling fowl of the problem. Constitution, brain, part, bundle, soul and nihilistic theories all have difficulties avoiding apparent entities other than the one that we presume is doing the thinking.
Olson provides a strong critique of immaterialism. There are three arguments offered in favor of immaterialism. First, the divisibility argument suggests that material things can be divided into parts, but thinking things are not divisible, therefore thinking things are immaterial. Olson suggests that there is no reason to think that thinking things are indivisible. What grounds this? Second, the argument from disembodied survival states that it is possible for me to survive without my body. Olson argues that this assumes what it is trying to prove. Finally, the inadequacy of physicalism argument tries to show that physicalism cannot account for mental phenomena we take for granted. Olson says that we can no more account for mental phenomena on immaterialism. What is it for a soul to think? How does it do that?
The weakest of Olson’s objections to immaterialism is the second, that suggesting it is possible for me to exist without my body begs the question. The argument, more precisely, is: if my mind and body are identical then all the properties of one are the same as the properties of the other. However, if there is one property that one thing has, but the other doesn’t then it is not identical (my mind possible exists when body doesn’t is the candidate property). It follows that my mind and body are not identical. One can deny modal properties or deny that it is conceivable that I can exist without the body existing, but if you accept modal properties and you can conceive of existing without your body then it is necessarily true that you and your body are not identical.
However, it would remain open to say that it is not possible to conceive of existing when our bodies do not. Materialists and Christians alike who say that they cannot conceive of their existing without their bodies or in a different body have suggested this. Perhaps it is impossible to conceive of a disembodied state. What would it be like to have no senses at all? How could that count as being conscious? It might be objected that one only must be able to conceive of being in another body other than one’s own. Amazingly, I can conceive of myself as a cockroach looking up at myself. This conception is the most likely candidate for an argument for immaterialism. Olson’s strongest response is that we have no idea what an immaterial soul is. Much more is known about the animal we appear to be identical to. This, according to Olson, should count in the materialist’s favor.
Eric Olson, What Are We? A Study in Personal Ontology (Oxford: OUP, 2007)