Doubt and certainty › Trying the Exercise Yourself

You do not have to accept Descartes' metaphysics to test the structure of his inquiry. Choose one belief you ordinarily take for granted. Identify what supports it, then distinguish a reason for doubting that support from a reason for believing the opposite. For example, discovering that a photograph has been edited can remove one reason for accepting the event it appears to show. That discovery alone does not prove that the event never happened. Other evidence could still support it. This is an everyday analogy for the difference between withholding assent and asserting falsity, not a claim that Descartes' method is an ordinary fact-checking procedure. Next, ask what a proposed conclusion actually establishes. Evidence that an experience occurs is different from evidence that the object of the experience exists as presented. Descartes uses that distinction when he treats sensing, considered as an act of thought, as certain even while doubting the bodies supposedly sensed. Finally, keep track of dependencies. If a later result depends on an earlier premise, an objection to that premise affects the later result as well. In the *Meditations*, the arguments about God, the reliability of clear and distinct judgment, and the existence of bodies are connected. Reading each as an isolated slogan obscures those connections.