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 simulta… - Jean-Jacques Rousseau

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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.