Pyrrho of Elis, a Greek philosopher who lived in the 4th century BC, is widely regarded as the founder of skepticism.

Skeptics argue that all knowledge is uncertain because our senses can be deceived, our reason is fallible, and our beliefs are often based on prejudice or tradition.

Skeptics have developed a number of arguments against the possibility of knowledge, including the regress argument, the evil demon argument, and the dream argument.

The regress argument argues that all knowledge is based on other knowledge, and this leads to an infinite regress. For example, we know that 2 + 2 = 4 because we learned it from someone else, who learned it from someone else, and so on. But if we ask where the original knowledge came from, we will eventually reach a point where we cannot answer the question.

The evil demon argument argues that there could be an evil demon who is deceiving us about everything. This demon could be so powerful that we would never be able to tell that we were being deceived. Therefore, we can never be sure that anything we know is true.

The dream argument argues that we can never be sure that we are not dreaming. When we dream, we often experience things that seem real, but when we wake up, we realize that they were not. Therefore, we can never be sure that what we are experiencing right now is not a dream.

Pyrrho of Elis, Arcesilaus of Pitane, and Carneades of Cyrene were all skeptical philosophers who lived in the Hellenistic period.

Arcesilaus of Pitane founded the skeptical school of thought known as the Academy.

Aenesidemus, Agrippa, and Sextus Empiricus were all skeptical philosophers who lived in the Roman period.

Aenesidemus founded the skeptical school of thought known as the Pyrrhonists.

Sextus Empiricus developed a number of skeptical arguments against the possibility of knowledge, including the modes of skepticism.

The modes of skepticism are a set of ten arguments that Sextus Empiricus developed to show that all knowledge is uncertain.

Michel de Montaigne, David Hume, and Immanuel Kant were all skeptical philosophers who lived in the modern period.

Michel de Montaigne did not found a skeptical school of thought.

David Hume developed a number of skeptical arguments against the possibility of knowledge, including the problem of induction.