 Skepticism is a philosophical activity of investigation characterized by the notion of suspension of judgment. Whereas dogmatists affirm or deny a proposition on a given philosophical topic, skeptics neither affirm nor deny any proposition, i. e., they remain uncommitted to any dogmatic doctrine. According to skeptics, the basic opposition in philosophy is that between those who endorse a philosophical theory and those who, after having inquired into the truth, did not find an answer to the questions under examination. That is why skepticism came to be seen by dogmatic philosophers as a major challenge to their philosophical project of finding the truth. Epistemologists and metaphysicians alike set themselves the task of overcoming skepticism in order to establish their own doctrines. Thus, one constantly finds dogmatic philosophers trying to refute the skeptic. One criterion to accept a philosophical proposal is to determine to what extent it overcomes the skeptical challenge.