I endeavor to determine exactly what Peirce's thesis of the iconicity of thought means and implies and how far it can be maintained. In particular, I argue that while for Peirce necessary reasoning requires an iconic dimension in order to be carried out, it does not follow that this is true of reasoning in general. I then suggest a way in which the thesis that 'it is by icons only that we really reason' could be defended on the basis of Peirce's philosophical system. I consider difficulties of the conception of thought upon which this defense is based, namely, that thinking is processual in nature and that our thoughts are in continuity with each other. More specifically, I argue that this view generates a tension within Peirce's system, and I reject it on the basis of Geachian arguments that, at the same time, shed new light on Peirce's most insightful claims concerning the nature of thought.