He decides to adopt a doubting frame of mind to free himself of the methods of thought he has up to now been accustomed. He will reject everything he previously held as true as long as it contained any element of falseness in it. Then if he can find one thing of which he is certain, he can start anew and build from the foundations up.
Descartes is forty years old and living in Holland. He has put off this endeavor until he has reached a mature age but an age when he can postpone it no longer. He now has the necessary solitude to begin his pursuit.