In the “Principles of the Civil Code,” Jeremy Bentham identifies four “principles subsidiary to utility”: subsistence, abundance, equality, and security. Whereas these subsidiary principles form part of the bedrock of classical liberalism, in this essay I show that in the hands of his friend and disciple William Thompson, they are transformed into the foundations for socialism. Where Bentham prioritizes security over equality, and security of property takes a preeminent role, Thompson shows that the system of individual competition and private property—his way of describing capitalism—is best characterized by the “inequality of security.” Based on the labor theory of property, Thompson argues that the system that assigns ownership to the providers of capital violates the workers’ security—the right to have the full produce of their labor secured to them. Thompson then reconciles security and equality, understanding them as mutually constitutive instead of in conflict. From his work I identify a modified set of subsidiary principles that place security and equality at the same level, and then adds additional subsidiary principles as necessary conditions to enable full equality of security: voluntarism, democracy, and united effort/common property. With this as his basis, Thompson offers the outlines for important elements of socialist theory, including the theory of surplus value; a call for the abolition of private property; and full equal social, civil, and legal rights for women, establishing a firm grounding for socialism in utilitarian philosophy. Because Thompson also was a major influence on the early cooperative movement, which also adopted these principles, this has significant implications for how we view the cooperative movement, which today may justifiably claim to be the world’s largest democratic social movement.