Was Charles S. Peirce a ‘naturalist’? If one has a look at the literature on Peirce, it seems that there is not a straightforward answer to this question. Some interpreters argue that he clearly is a naturalist, 1 but perhaps of a very original sort. Some others instead claim that there are elements in his thought that are incompatible with a naturalist perspective. 2 Of course, it is not surprising that scholars disagree on how to interpret a particular philosopher. However, as far as the disagreement about Peirce’s naturalism is concerned, this is partly dependent on the ambiguity of the term naturalism itself. For when interpreters ask whether Peirce is a naturalist or not, they often do not have the same question in mind. The question is alternatively taken to ask: whether Peirce regarded the method of the natural sciences as the only one able to deliver genuine knowledge; 3 whether Peirce envisioned the need for a ‘first philosophy’ in his system; 4 whether his rejection of psychologism was compatible with naturalism; 5 whether his account of mind and intentionality implies that these phenomena are part of or in continuity with nature; 6 whether he saw knowledge as a natural process; 7 whether he could be considered an anti-metaphysical philosopher. 8 The list could probably be much longer. For my purposes, it is sufficient to emphasise how a positive answer to one of these questions need not necessarily imply a positive answer to all of them. Therefore, when one interpreter is stressing that Peirce is a naturalist with respect to one of these questions, she is not necessarily contradicting another interpreter who says the opposite, but with respect to a different question in the list.