Why did Hobbes think promises needed enforcement by a sovereign?

Thomas Hobbes argued that promises in a social contract require enforcement by a sovereign because he viewed human beings as fundamentally rational and self-interested. In his work Leviathan, Hobbes posited that individuals in the state of nature would not keep their promises if doing so conflicted with their own interests.12

Because the state of nature is a condition of constant competition and war, Hobbes believed that the mere act of making a promise carries no weight. To ensure peace and prevent a return to a "solitary, poor, nasty, brutish, and short" existence, individuals must surrender their power to a sovereign authority. This sovereign—whether a monarch or an assembly—possesses the necessary power to punish those who breach their agreements. By creating a credible threat of punishment, the sovereign makes it rational for individuals to keep their promises, thereby establishing the foundation for justice and civil society.12