Most philosophers believe that a unified philosophical account of mental and non -mental actions is possible. This article presents two arguments indicating that in fact it is not possible. The first one says that thinking is not an activity. Its formulation, however, is exposed to significant difficulties. The second argument avoids these difficulties and puts forward a different, though sometimes erroneously identified, thesis that mental and non-mental actions differ significantly, and therefore one theory should not be expected to include both phenomena. Acceptance of this result sheds new light on the problems associated with the language of thought and gives promise to a new answer to the question “What is Le Penseur doing?”