The battle to secure mental stillness must first be fought and won before the battle of the ego can be brought to an end. For it is only in that deep state wherein all other thoughts are put to rest that the single thought of "I" as ego can be isolated, faced, fought until its strength is pitilessly squeezed out and destroyed at last. The attainment of this inner stillness is yoga; this conquest of the ego in it and after it is philosophy.
-- Notebooks Category 20: What Is Philosophy? > Chapter 1: Toward Defining Philosophy > # 13