What makes Lisp...Lisp?

If you starting removing features from Lisp, at what point is it no longer Lisp? Some people claim Clojure shouldn't be considered a Lisp. Is it because too much Lisp was removed?

What is at the very heart of Lisp that makes it Lisp?

>>35
He could implement a generic one by disregarding the type system, implementing some sort of LispObject's with type tags, and do a lot more greenspunning, or he could just use Lisp.