 One thing to note in passing is that skeptical scenarios like the evil demon or the brain in the vat did not seem to figure in the debate between the Stoics and Skeptics. The Skeptics press the point that at the time the dream may be completely convincing to the dreamer, even if she does not believe that the events actually transpired when she awakes (Cicero, Lucullus or Academica II, 88). They do not consider thought experiments in which all our sense experience is systematically misleading. But if we set this aside, there will still be one important difference between a clear and distinct impression that arises from a real fireplace and one that arises from the manipulation of my neurons by unscrupulous brain scientists. The first is caused by a fireplace, while the second is caused by some other means. When the Stoics say that a cognitive impression is “of such a sort as could not arise from what is not,” they can be interpreted to mean simply that the true clear and distinct impression will be different from a false one. Nothing said thus far by the skeptics rules out the possibility that we have a mechanism that has potential to become sensitive to these differences. They might deny that the difference between the two is always something that can be discerned from the subject’s point of view. We do not have a firmer means of knowing by virtue of which we check candidate impressions to see if they are really cognitive or not. Rather, we have the potential to increase our sensitivity to cognitive impressions when they are present.