There seems to be a tension between determinism and moral responsibility such that, if determinism is true then perhaps we cannot be responsible for our actions. In his On What Matters, Derek Parfit tried to find a way to dissolve this tension through discussing a Kantian argument about the noumenal world. In recent years Parfit’s argument has received some criticism, which has sought to undermine his argument while also making a variety of different claims about his actual views on this issue. In this paper, I argue that Parfit’s argument requires modification: and my proposals not only promise to make his argument clearer, but can also be used to answer some of his critics. I conclude by setting out a coherent argument—based on Parfit’s writings—for defusing the tension between determinism and moral responsibility. We will see that the truth of determinism is not a threat for moral responsibility—at least in some senses.