When is a concept a priori?

According to Michael Thompson's defence of neo-Aristotelian naturalism in meta-ethics, (i) ‘[t]he concept life-form is a pure or priori, perhaps logical, concept’, and (ii) human, as we human beings have it, an priori concept’ (p. 57). Here I show argument for be unsound, hoping thereby shed light on the neglected subject prioricity concepts more generally.