Is there, despite everything, a way out of doubt? Is there perhaps some assurance that the presupposition we have acknowledged as necessary is actually fulfilled? It would be vain to hope for any "proof" of this; proofs would only offer new points for radical skepticism to attack. No. The only thing that can help us is to present something that is exempt in advance from any doubt, that is, a fact. If there is such a fact, then the skepticism that put us on its track was not fruitless; it will have served to bring to light certain basic data of consciousness whose immeasurable significance might otherwise not have been correctly recognized and turned to account.