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