Bill asked:

What is the "modal argument" in relation to dualism?

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There are two meanings to the word "modal", one being that of mode or attribute and the other to do
with the modalities of possibility and necessity.

Descartes' used the former, but to make a successful claim for a real or ontological distinction, he
really needs the latter but this was not available to him since he didn't successfully establish
substantial difference. Descartes found that he had a clear idea of himself as a thinking thing, and
having established that clear and distinct ideas are grounds for knowledge, he also found he had the
clear idea of body as essentially extended and so he concluded that his was essence was a
non-extended thinking thing. The argument makes use of the assumption that attributes or modes
distinguish substances. However, it is not impossible for one substance to have two irreducible and
conceptually distinct attributes. Gilbert Ryle's category distinction, for instance, shows that a
university can be an institution and a campus, the campus being extended while the institution is not.
Peter Strawson has argued that a single substance can have physical and mental attributes which
receive different predicates without any implication of substantial dualism.

In the other sense of the modal, it might be argued that if two things are identical, one could never
exist without the other or, conversely, if two things are non-identical there are no circumstances under
which they could be the same thing. In a possible world thought experiment, it is certainly conceivable
that I could have a different body than the one I in fact have, but it wouldn't follow from this that I
could exist without any body and whichever body I do have, I could be identical to it and not exist
without it. However, it is logically for a person to survive the destruction of his body, and conceivable
that there are soul-substances. Yet, on the hand, the thought experiment lacks clarity. So again, the
dualist would need to look at essence, and argue that whichever body I have, the body is not me, but
I have a subjective essence, or personal identity which is mental and that makes me "me".

Rachel Browne

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