Alain Badiou’s The One: Descartes, Plato, Kant, translated by Jacques Lezra and Susan Spitzer, with an insightful introduction by Kenneth Reinhard, is a seminal work that offers an exploration of the philosophical concept of oneness through the lens of three major figures: Descartes, Plato, and Kant. This text is part of Badiou’s extensive lecture series, marking a crucial moment in his philosophical trajectory and one of the first of his seminars to be published.
Badiou, a prominent figure in contemporary philosophy, challenges the traditional metaphysical preeminence of “the One,” proposing instead his ground-breaking concept of the multiple. His lectures from 1983-1984, documented in this volume, form a vital foundation for his later, more expansive works, particularly Being and Event. In The One, Badiou meticulously examines the idea of oneness in the works of Descartes, Plato, and Kant, revealing its role as a counterpoint to his thesis that being is fundamentally multiple.
Central to Badiou’s ontology is the distinction between “the One” and “counting as one.” Through mathematical set theory, Badiou articulates that while a set is a collection of elements that can be operationally treated as one for mathematical purposes, this does not imply an ontological unity. This distinction is pivotal in Badiou’s argument against the traditional notion of a fundamental unit of being.
In his sessions on Descartes, Badiou goes deeply into the Meditations on First Philosophy, critically analysing Descartes’ proof for the existence of God. Badiou interprets Descartes’ introduction of subjectivism as a significant departure from hierarchical views of the world, initiating modern philosophy. However, Badiou points out that Descartes’ reliance on God as a guarantor of truth represents a failure to fully embrace the implications of his own subjectivist revolution. Badiou argues that Descartes’ inability to consider the “causality of lack” precluded the possibility of recognizing the multiple’s non-hierarchical nature, an insight essential for a modern ontology.
Badiou’s examination of Plato focuses on the Sophist and the Parmenides, dialogues that address the conflict between sophistry and philosophy and the complex nature of being. Badiou aligns himself with Plato’s struggle against sophistic nihilism and his endeavor to articulate an ontology that accommodates nonbeing. Through a rigorous analysis of the Parmenides, Badiou underscores Plato’s rejection of both monism and dualism, advocating instead for a conception of being as “counted as one,” prefiguring Badiou’s own ontology of the multiple.
In the sessions on Kant, Badiou tackles the apparent divergence between Kant’s epistemology and ontology. While Kant famously restricts knowledge to phenomena, leaving noumena (things-in-themselves) unknowable, Badiou, drawing on Heidegger’s interpretation, suggests that Kant’s work is fundamentally concerned with the nature of being. Badiou contends that Kant’s distinction between thinking and knowing allows for an engagement with being that transcends empirical cognition, emphasizing the givenness of objectivity and the presence of being beyond structured experience.
Kenneth Reinhard’s introduction provides a lucid overview of Badiou’s philosophical journey, situating The One within the broader context of Badiou’s work and its evolution. Reinhard highlights how Badiou’s decision that “the one is not”—that being is irreducibly multiple—forms the core of his ontological project. This decision, while not an argument in the traditional sense, is a pivotal philosophical stance that underpins Badiou’s critique of monism and his advocacy for a non-hierarchical understanding of multiplicity.
The One: Descartes, Plato, Kant is an essential text for anyone seeking to understand Badiou’s philosophy. It offers rich, detailed analyses of three foundational thinkers while showcasing the nascent stages of Badiou’s key ideas. Badiou’s innovative readings, combined with his rigorous engagement with mathematical ontology, make this seminar an invaluable resource for both students and scholars of philosophy.
Through his lectures, Badiou provides not just an interpretation of historical philosophical texts but a critical framework that challenges and extends their legacy. His treatment of Descartes, Plato, and Kant reveals a profound engagement with the history of philosophy, reinterpreting and transforming their ideas to support his own philosophical innovations. This seminar stands as a testament to Badiou’s intellectual rigor and his commitment to advancing a philosophy that embraces the complexity and multiplicity of being.
Simon Gros 
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