Anyone who seriously intends to become a philosopher must once in his life withdraw into himself and attempt, within himself, to overthrow and build anew all the sciences that, up to then, he has been accepting. Philosophy – wisdom [sagesse] – is the philosophizer’s quite personal affair. It must arise as his wisdom, as his self-acquired knowledge tending toward universality, a knowledge for which he can answer from the beginning, and at each step, by virtue of his own absolute insights.
The meditator keeps only himself as having an absolutely indubitable existence, as something that cannot be done away with, something that would exist even though this world were non-existent. Thus reduced, the ego carries on a kind of solipsistic philosophizing. He seeks apodictically certain ways by which, within his own pure inwardness, an objective outwardness can be deduced.
Anything belonging to the world, any spatiotemporal being, exists for me that is to say, is accepted by me in that I experience it, perceive it, remember it, think of it somehow, judge about it, value it, desire it, or the like. Descartes, as we know, indicated all that by the name cogito. The world is for me absolutely nothing else but the world existing for and accepted by me in such a conscious cogito.
In these my whole world-life goes on, including my scientifically inquiring and grounding life. By my living, by my experiencing, thinking, valuing, and acting, I can enter no world other than the one that gets its sense and acceptance or status in and from me, myself.
Edmund Husserl – Cartesian Meditations