Habermas, Apel, and Kuhlmann all try to show that the skeptic's willingness to engage in rational argumentation unavoidably commits her to assume implicitly the validity of a certain moral principle. Thus, for all of the three philosophers, the structure of the argument is the same: it is in all cases a rationalistic argument. However, Habermas understands his argument as a universal pragmatic argument (or a weak transcendental pragmatic argument), whereas Apel and Kuhlmann understand their respective arguments as (strong) transcendental pragmatic arguments amounting to an ultimate justification (Letztbegründung).

It might be argued that because of this difference, Apel and Kuhlmann would have been more appropriate targets of my criticism in this book. I disagree. The aim of the book was to criticize the rationalistic assumption which they share. For this purpose, the difference between universal and transcendental pragmatic arguments is simply irrelevant. In addition, there is an important sense in which my own argumentative strategy in this book has more in common with transcendental pragmatic arguments than universal pragmatic arguments. The aim of this appendix is to explain the sense in which this is so. This will also allow me to explain how my approach and Habermas' represent two very different ways of allowing morality to be contingent in a way that Kuhlmann and Apel do not allow.

Kuhlmann argues that Habermas' theory is “empiricist” in a way which makes it impossible for Habermas to account for the unconditionality of morality.