Can be projected in the fields of decision and action, or affect only the belief, faith or the validity of knowledge. If you are above a "truth" conventionally accepted, the question implies uncertainty in the validity.
When doubt is accepted as ignorance can be a source of knowledge for the study and criticism.
In philosophy, skeptical doubt is equivalent to the suspension of the trial (epojé) attempting to cause, with its numerous and often sensible arguments, skeptics old (Pyrrhonism).
The skeptical arguments Descartes seem bizarre faces watched from everyday life and common sense. But Descartes does not seem to have confused the set of beliefs and convictions that clearly were needed to guide practice, the criteria of philosophical inquiry. This can be seen in Descartes's distinction between the Rules of the Method and Rules of the "provisional morality".
The research, which is a practical task and takes place in the general area of life, is intended to serve it, but it would be foolish to wait before she would reach some reasonably reliable results.
Meanwhile, to develop, the research is to submit for consideration a huge portion of what we call "common sense", meaning that many ideas according to which (it appears) we will live as long as the research itself operates.
But it is not stopping the practice and life to allow research, nor to pass off as "results", a mere intellectual fashions (the doctrine of the sect where we educate, or any other product of the confusion.) The Cartesian project was to examine these ideas, among others, in search of valid philosophical grounds.
The skeptical arguments (aimed at introducing doubt) that Descartes believes in the Meditations, have been taken as a whole of Plato (Cratylus and Theaetetus). These arguments are a research tool, and first assessed in accordance with whether or not intelligible, and if once accepted, would in principle be open to discussion (otherwise, would be incompatible with the research).
If both conditions are met, the arguments are useful to the philosophical enterprise in the opinion of Descartes (just as research tools). For later research in Cartesian, would judge whether we really have no reason to allow discarding.
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