BERTOLT BRECHT, The Threepenny Opera

Until philosophers are kings, or the kings and princes of this world have the spirit and power of philosophy, and political greatness and wisdom meet in one, and those commoner natures who pursue either to the exclusion of the other are compelled to stand aside, cities will never have rest from their evils — no, nor the human race, as I believe — and then only will this our State have a possibility of life and behold the light of day.

PLATO, The Republic

KARL MARX, The German Ideology

There are moments in life where the question of knowing whether one might think otherwise than one thinks and perceive otherwise than one sees is indispensable if one is to continue to observe or reflect ... What is philosophy today ... if it does not consist in, instead of legitimizing what we already know, undertaking to know how and how far it might be possible to think otherwise?

Shall I show you the sinews of a philosopher? "What sinews are those?" — A will undisappointed; evils avoided; powers daily exercised, careful resolutions; unerring decisions.

Each of the parts of philosophy is a philosophical whole, a circle rounded and complete in itself. In each of these parts, however, the philosophical Idea is found in a particular specificality or medium. The single circle, because it is a real totality, bursts through the limits imposed by its special medium, and gives rise to a wider circle. The whole of philosophy in this way resembles a circle of circles. The Idea appears in each single circle, but, at the same time, the whole Idea is constituted by the system of these peculiar phases, and each is a necessary member of the organisation.

GEORG WILHELM FRIEDRICH HEGEL, Encyclopedia of the Philosophical Sciences