existence

The assertion, explicit or implicit, of the existence of specific things is a feature of many ideas. If an idea asserts the existence of something then, assuming that idea is sufficiently true, the thing exists.

If the self is a rare, complex pattern of information in the multiverse with fascinating and important properties then the self exists. If the Self is a supernatural entity piloting a body then the Self does not exist.

If free will is the ability to creatively solve problems then free will exists. If Free Will is having supernatural/inexplicable powers then Free Will does not exist.