H. L. A. Hart in the context of "Alan Turing"

In legal philosophy, legal positivism is the theory that the existence of the law and its content depend on social facts, such as acts of legislation, judicial decisions, and customs, rather than on morality. This contrasts with theories such as natural law, which hold that law is necessarily connected to morality in such a way that any law that contradicts morality lacks legal validity.

Thomas Hobbes defined law as the command of the sovereign. This idea was elaborated in the 18th and 19th centuries by legal philosophers such as Jeremy Bentham and John Austin, who argued that a law is valid not because it is intrinsically moral or just, but because it comes from the sovereign, is generally obeyed by the people, and is backed up by sanctions. Hans Kelsen developed legal positivism further by separating law not only from morality, as the early positivists did, but also from empirical facts, introducing the concept of a norm as an "ought" statement as distinct from a factual "is" statement. In Kelsen's view, the validity of a legal norm derives from a higher norm, creating a hierarchy that ultimately rests on a "basic norm": this basic norm, not the sovereign, is the ultimate source of legal authority.In addition to Kelsen, other prominent legal positivists of the 20th century include H. L. A. Hart and Joseph Raz.

Ordinary language philosophy (OLP, sometimes called linguistic philosophy) is a methodological approach within analytic philosophy which treats many traditional philosophical problems as the result of misunderstandings of how words are ordinarily used. Rather than proposing ideal or artificial languages, ordinary language philosophers investigate the actual use of expressions in everyday contexts, and often argue that once such uses are described carefully, many philosophical "problems" dissolve or change their shape.

In the twentieth century OLP was primarily associated with the later work of Ludwig Wittgenstein, early to mid-century philosophers at the University of Cambridge such as G. E. Moore and John Wisdom, and mid-century philosophers at the University of Oxford, including Gilbert Ryle, J. L. Austin, P. F. Strawson, H. L. A. Hart, and Paul Grice. Because a number of its most prominent practitioners taught at Oxford, OLP is sometimes informally referred to as "Oxford philosophy".