customs. Skepticism can also be applied to knowledge in general. However, this attitude is usually only found in some forms of philosophical skepticism. A closely related classification distinguishes based on the source of knowledge, such as skepticism about perception, memory, or intuition. A further distinction is based on the degree of the skeptical attitude. The strongest forms assert that there is no knowledge at all or that it is impossible. Weaker forms merely state that one can never be absolutely certain. Some theorists distinguish between a good or healthy form of moderate skepticism in contrast to a bad or unhealthy form of radical skepticism. On this view, the "good" skeptic is a critically-minded person who seeks strong evidence before accepting a position. The "bad" skeptic, on the other hand, wants to "suspend judgment indefinitely ... even in the face of demonstrable truth". Another categorization focuses on the motivation for the skeptical attitude. Some skeptics have ideological motives: they want to replace inferior beliefs with better ones. Others have a more practical outlook in that they see problematic beliefs as the cause of harmful customs they wish to stop. Some skeptics have very particular goals in mind, such as bringing down a certain institution associated with the spread of claims they reject. Philosophical skepticism is a prominent form of skepticism and can be contrasted with non-philosophical or ordinary skepticism. Ordinary skepticism involves a doubting attitude toward knowledge claims that are rejected by many. Almost everyone shows some form of ordinary skepticism, for example, by doubting the knowledge claims made by flat earthers or astrologers. Philosophical skepticism, on the other hand, is a much more radical and rare position. It includes the rejection of knowledge claims that seem certain from the perspective of common sense. Some forms of it even deny that one knows that "I have two hands" or that "the sun will come out tomorrow". It is taken seriously in philosophy nonetheless since it has proven very hard to conclusively refute philosophical skepticism. In various fields Skepticism has been responsible for important developments in various fields, such as science, medicine, and philosophy. In science, the skeptical attitude toward traditional opinions was a key factor in the development of the scientific method. It emphasizes the need to scrutinize knowledge claims by testing them through experimentation and precise measurement. In the field of medicine, skepticism has helped the establishment of more advanced