Full Idea
Identity has a universality and basicness that is hard to overstate; concepts don't get more basic than this - or more indispensable.
Gist of Idea
Identity is as basic as any concept could ever be
Source
Colin McGinn (Logical Properties [2000], Ch.1)
Book Reference
McGinn,Colin: 'Logical Properties' [OUP 2003], p.9
A Reaction
I agree with this. It seems to me to follow that the natural numbers are just as basic, because they are entailed by the separateness of the identities of things. And the whole of mathematics is the science of the patterns within these numbers.