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Although he wrote extensively, Descartes chose not to publish his earliest efforts at expressing the universal method and deriving its consequences.
Free Essays on Descartes and the Cartesian Method
This approach is called the Method of Doubt, and Descartes likened it to 'that of a man who takes all the apples out of a barrel one by one, inspects them, and then puts the sound ones back' [Williams; p.59].
To begin understanding Rene Descartes’ method of doubt, you need to suspend all prejudice and prior judgments and start with a clean slate “for the purpose of discovering some ultimate truth on which to base all thought.” (Kolak, Pg.225).