The thesis upon which Peirce grounded the solution of the Antinomy of the Liar is (in my opinion) fundamental. This holds, not only with regard to the solution of the Liar, but also in respect of the relations between colloquial and formalized languages (as these are understood nowadays). Moreover, it can be shown that, owing to the same thesis, the very source of the concept of "true proposition" comes unexpectedly to light. These are the points which I would now like to explain.