The concept of truth is a fundamental category in the theory of knowledge and philosophy in general. Other philosophical categories presuppose the concept of truth as their content or as the goal of investigatory inquiry. Philosophy begins historically with rejection of any form of opinion in the name of truth and with the counterposing of what truly exists to the variety of appearance. Thus was born theoretical thought, for which in antiquity philosophy was a synonym.

On Islamic practices, doctrines and on Islamic ethics.