On 5 April 1971, the writer and philosopher Simone de Beauvoir, along with 343 other prominent women, publicly declared that she had had an abortion. At the time abortion was illegal in France and was punishable by up to five years imprisonment. By openly challenging the authorities, the women sought an end to a law that criminalised a practice that most women considered a natural right. The ‘Manifesto of the 343’ as it was called was one notable act in the broader Women’s Liberation Movement (MLF; Mouvement de Libération des Femmes) which gained momentum in France in the 1970s.Twenty years earlier, Beauvoir had cemented her position as a feminist thinker through The Second Sex (1949), a critical analysis of gender in society. In her book Beauvoir uses 19th-century German philosopher GWF Hegel’s notion that self-consciousness only becomes possible in relation to another self, the other. When we, as the subject, observe a stranger, our consciousness is realised only through what we see as their perception of us. Beauvoir argues that, similarly, woman has been historically defined as the other self to man. Man is the subject, the ideal; woman is only defined in reference to this ideal. Beauvoir blames society for this perception, for shaping women into a subordinate role: ‘one is not born, but rather, becomes a woman.’1To find a solution to this historical disparity, to allow women to break out of their secondary role, Beauvoir turns to existentialism, a philosophy most commonly attributed to writer Jean-Paul Sartre, a lifelong intellectual and romantic partner of Beauvoir. Existentialism recognises the intrinsic freedom that humans possess, the freedom to make choices. This freedom is always present: even a prisoner incarcerated in a cell can choose how to deal with life in prison.Beauvoir uses this principle of existentialism to argue that woman cannot be unequivocally subjugated because even a woman forced by society into a subordinate position still retains her existential freedom — just as much as a prisoner in a cell.However, Beauvoir does recognise a difference between existential freedom and a more practical freedom. In the real world, societal structures, such as anti-abortion laws, prevent women from having the same opportunities as men. Furthermore, much like a prisoner serving a lengthy term is unable to envisage life outside, women have become naturalised to their subordinate position. Given this reality, existential freedom through individual choices is inadequate, and Beauvoir urges collective action and political engagement to break down these institutionalised barriers. Women must ‘develop a political and social sense’, ‘take militant action [...] and have confidence in their future’.2Beauvoir’s ideas were influential in the anti-abortion campaign of April 1971. Women having control over their own fertility would allow them to be more than mere ‘slaves of the home’.3 The ‘Manifesto of the 343’ and the MLF’s campaigning eventually led to France legalising abortion in 1975.