As Apel himself notes in his preface, the expression Transformation of Philosophy bears an ambiguity, naming both a change that took place in the development of philosophy as well as Apel's own systematic project. As a historical approach the title characterizes the transformation that philosophy has undergone in 20th century philosophy through an emphasis on the mediation and the configuring power of language. Apel focuses on three main currents, represented by Wittgenstein, Heidegger, and Peirce.