Künne outlines Bolzano's attempt to give a definition of the concept of truth and asks whether Frege succeeded in showing that all such endeavours are doomed to failure. Bolzano and Frege are agreed that the schema "That p is true if, and only if, p' captures an important feature of the concept of truth, and in different ways both went beyond this observation: Frege maintained that the two halves of such biconditionals express the same proposition, and Bolzano (who explicitly denied this Identity Thesis) supplemented the equivalence schema with "If it is true that p then it is true because p'. Künne locates this true-because principle in Bolzano's general theory of grounding and explores whether Frege's Identity Thesis can be refuted by appealing to it.