Follower of Plotinius who developed neo-Platonism at Alexandria from about 400 to her death in 415. She was so well-known, apparently, that correspondence addressed only to "The Philosopher" is said to have reached her.
Also a leading mathematician and astronomer, she is thought to have taught ideas relating to different levels of reality and humanity's ability to understand them. She seems to have believed that everything in the natural world emanates from "the one" - and that human beings lack the mental capacity fully to comprehend ult imate reality.
Her subsequent obscurity probably reflects the fact that none of her work survives (although letters from a pupil do). It appears, however, that her influence made the city's Christian community feel threatened - perhaps partly because of her emphasis on the value of science. She was torn to death by a Christian mob (including monks armed with oyster shells). Admirers revere her as a philosophical martyr comparable to Socrates.
Hannah Arendt: 1906-1975
German-born Jewish philosopher who studied under Heidegger (with whom she also had a brief relationship) before being imprisoned by the Gestapo in 1933 for her work on anti-Semitic propaganda.
She escaped and fled to Paris; seven years later, following the fall of France, she moved to the US. Initial interests in existentialism and in the thought of St Augustine gave place to a more political awareness. She is best known for The Origins of Totalitarianism (1951), as well as for her coverage of Adolf Eichmann's trial (published first in The New Yorker and then in her 1963 book, Eichmann in Jerusalem: A Report on the Banality of Evil). Her justification for capital punishment in Eichmann's case was that, as Eichmann had not wanted to share the earth with the Jews, the Jewish state had no reason to share the earth with him. The first two volumes of her projected three-volume Life of the Mind were published posthumously, as was her Reflections on Kant's Political Philosophy.
Simone de Beauvoir: 1908-1986
Undeservedly overshadowed by her lover, Jean-Paul Sartre, Beauvoir developed an education in traditional philosophy (she wrote a thesis on Leibniz) into more radical explorations of feminism and existentialism.
Some of her ideas - about human freedom, for example, and about "being-for-itself" and "being-in-itself" - overlapped with Sartre's, but her best philosophical work, such as The Ethics of Ambiguity (1948), was important in its own right, as was her towering work of feminist ideology, The Second Sex (1949). In The Second Sex, Beauvoir argues that women have been held back throughout history by the perception that they are a "deviation" from the male norm - an assumption that must be broken if feminism is to succeed.
Elizabeth Anscombe: 1919-2001
Oxbridge-rooted academic principally concerned with defining the actual nature of phenomena such as mind and morality, Gertrude Elizabeth Margaret Anscombe has been described as the pre-eminent British philosopher of the 20th century. She had intellectual roots not only in classical philosophy but also in Roman Catholicism and in the modern philosophy of Wittgenstein and Frege. A friend of Wittgenstein, she produced the definitive (and still unrevised) translation of his Philosophical Investigations in 1953, as well theIntroduction to Wittgenstein's Tractatus in 1959. Her Intention (1957) is considered to be the founding document of modern "action theory". An analytical philosopher of exceptional rigour, she allegedly once said to A J Ayer: "If you didn't talk so quickly, people wouldn't think you were so clever"; to which the philosopher replied: "If you didn't talk so slowly, people wouldn't think you were so profound."
Anne, Lady Conway: 1631-1679
An English follower of Descartes with an interest in the kabbala and, later, Quakerism.
Born Anne Finch, she studied philosophy secondhand - via her brother - under Henry More at Cambridge. Her sex debarred her from studying the subject herself, but she corresponded with More for most of her relatively short life - she died at the age of 47.
Preoccupied with the question of substance - she doubted the existence of inert matter - she developed a God-based theory of nature as an integrated mental and material order ("life and figure are distinct attributes of one substance"), made up of individual "monads".
In this, she anticipated Leibniz, who acknowledged her as an influence. Her one surviving work, Principles of the Most Ancient and Modern Philosophy, was published posthumously (and anonymously) in 1690.
Anne Conway suffered from severe migraines and is said to have considered the operation known as trepanning as a possible cure.
Sarah Margaret Fuller: 1810-1850
US-born feminist and champion of transcendental idealism, whose Woman of the Nineteenth Century was America's first major feminist manifesto. A pupil of Emerson, she taught in Rhode Island and Boston before moving to Europe in 1846 and marrying an Italian aristocrat. Together with her husband and son, she drowned off Fire Island, New York, after fleeing the Italian revolution.
Susan Haack: 1945-
British-born professor of philosophy and law at the University of Miami. Inhabits the difficult end of the spectrum, propounding an epistemological theory called foundherentism, a kind of Third Way between foundationalism and coherentism. (If you need to ask, you wouldn't understand.) Works include: Deviant Logic (1974), Philosophy of Logics (1978), and Defending Science - Within Reason Between Scientism and Cynicism (2003).
Mary Wollstonecraft: 1759-1797
English feminist and egalitarian, associated with Thomas Paine and William Godwin (her husband). A Vindication of the Rights of Men (1790) argued against the slave trade; A Vindication of the Rights of Women (1792) did what it said on the jacket. Described marriage as "legal prostitution". Opposed monarchy, church and military. Died after giving birth to the future Mary Shelley.
Ayn Rand: 1905-1982
Controversial Russian novelist and philosopher, a "radical capitalist" whose works are popular with young Tories (and Camille Paglia). Moved to US in 1924 and developed a philosophy of individualism she called Objectivism ("a philosophy for living on earth"). Best-known works: The Fountainhead (1935) and Atlas Shrugged (1957). Appeared in a Tobias Wolff memoir, and was played by Helen Mirren in a 1999 film about her life.
Dame Mary Warnock: 1924-
Mary Warnock has significantly more influence on the way British society thinks of itself than any living male philosopher. She is a champion of a woman's right to philosophise. A veteran of royal commissions and committees of inquiry, she has published (among much else) The Uses of Philosophy (1992), and Women Philosophers (1996).
Profiles by Ellie Levenson