As it is common to justify classifications or whole scientific theories in a process of equilibrium in comparison with observations and their agreement with predictions, the attempt now is to justify even abstract cognitive processes in a reflective equilibrium appealing to the linguistic practice. But, contrary to the sciences, philosophy cannot invoke the confirmation of a prediction to guarantee the rationality of its practice. That is why we are again appealing to common sense in order to guarantee the reliability of philosophy. This is the reason for seeing what can be understood by “common sense”.