In an interview with Karl-Otto Apel, conducted and published by Florian Rötzer in 1987, a number of issues of Apel’s transcendental-pragmatic philosophy were discussed. The interview presents what was the subject of the main debates conducted at the time by this defender of reason and rationalist tradition in philosophy, who spoke out against all radical scepticism and was known above all as a philosopher defending the thesis of the need and the possibility of providing ultimate justification. Karl-Otto Apel explains how this thesis should be understood and what the transcendental-pragmatic ultimate justification consists of. The interview also expounds what is the argument of performative self-contradiction that is used in the final justif...