| When René Descartes describes ideas as being clearly and distinctly true, he means that their truth flows from logic, and that the conclusion is necessarily true given the facts. Some truths are, furthermore, self-evident and do not depend on external facts for their proof. Certain statements like "I exist" are necessarily true because such a situation where they were false is impossible and contradictory.
Descartes idea of clear and distinct perception is only valid when applied to ideas within a logical context. Concepts are defined in such a way as to allow their combination in arguments, and when those arguments allow no room for logical error, then the conclusion is said to be perfectly true. That this conclusion depends on the veracity of the original concepts is accepted; surely if they change then a perfect conclusion must likewise be altered. But the supposition arrived upon is also dependent on the method of deduction, and to presume this method to be perfect and unalterable is presumptuous. Therefore, argument and logical deduction are only truly valid concerning their own creations; although concepts that are defined with certain logical ideas can be perfectly arranged within that logical framework, there is nothing to ensure that these ideas have any relation with anything outside this specifically defined universe.
When Descartes, or anyone, makes a statement such as "I exist", or "2+2=4", they are assuming definitions for each of the items in their argument, and are likewise making certain assumptions about the nature of logic. These assumptions are widely agreed upon, and generally taken as self-evident, but are likewise defined in terms of their relationships. Thus, 2 + 2 is defined as 4, and 4 is defined as the combination of defined numbers. We have no real way of concluding their accuracy from any source external to our sphere of logic. Descartes admits that even such statements as "I exist" might be incorrect, "I cannot but admit that it would be easy for God, ...to bring it about that I go wrong even in those matters which I think I see utterly clearly with my mind's eye." ( Meditation III P. 4) So to prove the truth of his deductions, it becomes necessary for Descartes to prove the existence of a God who does not wish us to be deceived. The arguments that Descartes uses to prove the existence of such a God] are mistaken on two accounts. The first being that the arguments he uses must necessarily be prone to the same possibilities of deception as any other arguments, and therefore a God who wishes him deceived might secure a false conclusion by Descartes by the same tricks Descartes is attempting to rule out. The second is Descartes belief that something cannot come from nothing, or rather that only imperfection can be added in creation, even in the creation of thought. This is the basis for his argument of a perfect being, whose definition includes a desire against deception, and is similarly used with regard to clear and distinct perception, "every clear and distinct perception is undoubtedly something, and hence cannot come from nothing, but must necessarily have God for its author." (Meditation IV) Descartes fails to back up this type of reasoning, beyond its truth being supposedly clearly and distinctly perceived, and it is in this circular logic that his definition and use of this perception finally fails.
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