 The term scepticism (skepticism) has at least three distinct usages that are relevant for the discussion on pseudoscience. First, scepticism is a philosophical method that proceeds by casting doubt on claims usually taken to be trivially true, such as the existence of the external world. This has been, and still is, a highly useful method for investigating the justification of what we in practice consider to be certain beliefs. Secondly, criticism of pseudoscience is often called scepticism. This is the term most commonly used by organisations devoted to the disclosure of pseudoscience. Thirdly, opposition to the scientific consensus in specific areas is sometimes called scepticism. For instance, climate science deniers often call themselves “climate sceptics”. 