The aim of this paper is to explore the hypothesis that mental concepts are natural kind concepts. By ‘mental concepts’ I mean the ordinary words belonging to our everyday languages that we use in order to describe our mental life. The plan of the paper is as follows. In the first part, I shall present the hypothesis: firstly, I shall present a theory about the meaning of natural kind concepts following Putnam's 1975 proposal, with some modifications; secondly, I shall present (...) a taxonomy of mental concepts and, thirdly, I shall explain what the meaning of each kind of mental concept would be on the hypothesis defended in this paper. In the second part of the paper, I shall present two interesting consequences of the hypothesis proposed: first, that it is preferable to avoid a certain way of conceiving phenomenal concepts which does not fit with the hypothesis proposed; second, that folk psychology could fruitfully be considered a theory, and why, ultimately, it will not be eliminated. (shrink)