La jeunesse est le temps d'étudier la sagesse; la vieillesse est le temps de la pratiquer. - Jean-Jacques Rousseau

At first our pupil had merely sensations, now he has ideas; he could only feel, now he reasons. For from the comparison of many successive or simultaneous sensations and the judgment arrived at with regard to them, there springs a sort of mixed or complex sensation which I call an idea. The way in which ideas are formed gives a character to the human mind. The mind which derives its ideas from real relations is thorough; the mind which relies on apparent relations is superficial. He who sees relations as they are has an exact mind; he who fails to estimate them aright has an inaccurate mind; he who concocts imaginary relations, which have no real existence, is a madman; he who does not perceive any relation at all is an imbecile. Clever men are distinguished from others by their greater or less aptitude for the comparison of ideas and the discovery of relations between them. Simple ideas consist merely of sensations compared one with another. Simple sensations involve judgments, as do the complex sensations which I call simple ideas. In the sensation the judgment is purely passive; it affirms that I feel what I feel. In the percept or idea the judgment is active; it connects, compares, it discriminates between relations not perceived by the senses. That is the whole difference; but it is a great difference. Nature never deceives us; we deceive ourselves.

Nowadays, when more subtle studies and more refined taste
have reduced the art of pleasing into principles, a vile and
misleading uniformity governs our customs, and all minds seem
to have been cast in the same mould: incessantly politeness
makes demands, propriety issues orders, and incessantly people
follow customary usage, never their own inclinations. One does
not dare to appear as what one is. And in this perpetual
constraint, men who make up this herd we call society, placed in
the same circumstances, will all do the same things, unless more
powerful motives prevent them. Thus, one will never know well
the person one is dealing with.

No hay día que no recuerde con gozo y ternura aquel único y breve tiempo de mi vida en que fui plenamente yo, sin mezcla y sin traba, y en que puedo realmente decir que he vivido.