  The existence of the special character alleged to distinguish cognitive impressions from other impressions was the principal target of the Academics’ arguments (see Section 3 of the entry on  Carneades).   If such impressions do not exist, it follows immediately in the context of Stoic epistemology that nothing can be known. On the basis of this result and the Stoic doctrine that the wise, i.e., human beings as they ought to be, do not hold (mere) opinions (S.E. M 7.155–7), the Academics went on to argue that one ought to suspend judgement about all matters.