Philosophical skepticism is a family of philosophical views that questions the possibility of knowledge. It is a doubtful attitude toward commonly accepted knowledge claims and is an important form of skepticism. Skepticism in general is a questioning attitude toward all kinds of knowledge claims. Philosophical skepticism differs from other forms of skepticism in that it even rejects very plausible knowledge claims that belong to basic common sense. Skepticism can be directed at beliefs about the existence of some supposedly problematic entity, such as the self or God. Skeptical hypotheses are propositions that, if true, would undermine our knowledge of some domain. Skeptical hypotheses are used to argue that knowledge is impossible. Skepticism can be global, which questions the possibility of all knowledge, or local, which questions the possibility of knowledge only in particular areas of study. Philosophers who wish to overcome philosophical skepticism must find reasonable grounds for rejecting the skeptics argument.