For the witch, the seat of magic is the mind.

Animals know. Human beings know that we know. The wise know that we know that we know: we can observe our own thought processes. And the witch is the one who can consciously and with intent aforethought manipulate her own thought processes. (Terry Pratchett, that not un-astute observer of witchdom, calls this “having third thoughts.”) The witch knows that it's not good enough to think: Oh well, that's how I think, so that's that. The witch thinks: Hmm, that's how I think; how do I think myself into thinking differently?

And that's the heart and pulse of all our magic.