What makes a thing the thing it is, rather than something else? What makes it the kind of thing it is, rather than something else entirely? Anything at all?
I think there’s something that makes humans human, numbers numbers, colours colours. It’s hard to say exactly what it is that makes humans human. I’m much more confident that it’s something, rather than nothing at all.
I don’t think these questions are idle speculation. They play a central role in our metaphysical theories of the world. Just what are material objects? What are abstract mathematical objects? For me, the best way to pursue these questions is by first developing a theory of the essences or natures of things, which makes them the very things they are.
Along with my colleague Steve Barker, I’ve developed a theory of material objects. We call it Essential Bundle Theory. I quite like it: I think it answers a lot of the questions I was asking about the fundamental make-up of the material world. It also helps answer questions abut metaphysical necessity and possibility: the ways things might have been.
There’s a consequence of the view I find puzzling: it doesn’t rule out the possibility that each of us could have been someone else. It allows for contingent identity statements, whereby a statement like a = b is true but possibly false, or false but possibly true. That’s a view many find highly puzzling, or even incoherent. Part of this project is to develop the metaphysics and logic of contingent identity statements, so as to demonstrate their coherence.
Besides, I quite like the idea that I could have been you. It gives me (extra) reason to consider your wellbeing and generally work at not being a dick to others.