Descartes' Second Rule of the Direction of the Mind is: He then continues... There is more to it, which I will post if I see it necessary, but that is basically what he is trying to say. The point of this thread is to determine the level of certainty that is "healthy". There are those that would have you embrace a complete Uncertainty, in which absolutely nothing is certain (a concept which I believe to be paradoxical, much in the same way as Limitlessness is paradoxical (and this too may be discussed in this thread)). However, there are others who would have you accept some things as certain, and use those things as foundations for progressing in knowledge. Perhaps there are even some who agree with Descartes' (as quoted above), that we should not trouble ourselves with things that are merely probable, but should stick to that which can be readily demonstrated as factual.