The task that Hume explicitly sets himself in 3.2 of the Treatise is to identify the motive that renders just actions virtuous and constitutes justice as a virtue. But surprisingly, he never provides a clear account of what this motive is. This is the problem of the missing motive. The goal of this paper is to explain this problem and offer a novel solution. To set up my solution, I analyze a recent proposal from Geoffrey Sayre-McCord and illustrate what it (...) gets right and what it gets wrong. I develop a solution that retains the benefits of his proposal while addressing its defects. The result is a significant advancement in our understanding of Hume’s theory of justice. (shrink)