Descartes held the view that a subject has infallible beliefs about the contents of her thoughts. Here, I first examine a popular contermporary defense of this claim, given by Burge, and find it lacking. I then offer my own defense appealing to a minimal thesis about the compositionality of thoughts. The argument has the virtue of refraining from claims about whether thoughts are “in the head;” thus, it is congenial to both internalists and externalists. The considerations here also illuminate how a subject may have epistemicially priviledged and a priori beliefs about her own thoughts.