Edinburgh born philosopher David Hume (1711- 1776) is the man who captured the essence of skepticism. His works built on and formulated the concepts of scepticism, empiricism and naturalism. His most famous works were "A Treatise of Human Nature" and "An Enquiry Concerning Human Understanding". In these books he tried to understand human perceptions and how human beings perceive the world. He held that passion rather than reason governs human behaviour and that the sciences are constantly filtered through human nature and human experience and the better we understand them to remove or counteract these filters, the better we can understand reality. He formulated the is/ought problem - because something IS some way, it does not follow that it OUGHT to be that way. He had a profound influence on ethics and moral teachings as a result.
He also wrote extensively on religion and was criticised for being an atheist/agnostic. His writings were very critical of religious superstition and dogma and his most famous quote on the subject was a damning critique of miracles (which he defined as: "a transgression of a law of nature by a particular volition of the deity, or the interposition of some invisible agent."). Hume wrote: "...no testimony is sufficient to establish a miracle, unless the testimony be of such a kind, that its falsehood would be more miraculous, than the fact, which it endeavors to establish." It is a simple line that should be understood by skeptics everywhere. The more pithy version by Carl Sagan was "Extraordinary claims require extraordinary evidence"
Hume's statue was erected in 1997 and stands on the Royal Mile outside the High Court. Ironically over the years the big toe is being worn smooth by the constant touchings by students, especially philosophy students, before exams 'for good luck'. A practice now picked up by tourists and visitors. Hume as a staunch critic of superstition and irrationality would likely be appalled.