on quotation

Some über-obvious notes:

Lisp literals (booleans, numbers, strings, ...) are sometimes called self-evaluating or self-quoting objects.

This is important because it brings to mind that other objects don't evaluate to themselves: a symbol evaluates to the value of the variable it names, and a list evaluates to the result of a call.

To actually get hands on a symbol or list, we need to quote it. Literals need no quoting, they're self-quoting.

While unquoted X looks quite similar to quoted 'X, they're utterly different. X stands for read a variable from memory, while 'X stands for construct a symbol object with the name "X" (leaving interning aside).

And that's really the use-mention distinction.