From minerals to plants to animals to man the scientific quest advanced. Armed with the microscope, and spurred on by the needs of physicians, a growing fraternity of students peered into the human body, and found its organs and functions indisputably similar to those of the higher beasts. But there still seemed to be a break in the chain of being: nearly everyone agreed that the mind of man differed in kind, as well as degree, from the mind of animals.

In 1749 David Hartley, an English clergyman turned physician, ventured into the gap by founding physiological psychology. For sixteen years (1730–46) he gathered data; then, in 1749, he published his Observations on Man. Ambitious to find a principle governing the relations of ideas as Newton had proposed a principle governing the relations of bodies, Hartley applied the association of ideas to the explanation not only of imagination and memory, as Hobbes and Locke had done, but also of emotion, reason, action, and the moral sense. He pictured sensation as first a vibration in the particles of a nerve stimulated by an external object, and then as the transmission of this vibration along the nerve to the brain, like “the free propagation of sounds along the surface of water.”132 The brain is a mass of nerve fibrils whose vibrations are the correlates of memories; one or more of these fibrils is agitated by an incoming vibration associated with it in past experience; this reverberation is the physiological concomitant of an idea. For every mental state there is a corporeal correlate, and for every bodily operation there is a mental or neural accompaniment; the association of ideas is the mental side of the association of nerve vibrations aroused by their contiguity or succession in past experience. Hartley’s physiological picture was, of course, highly simplified, and never touched the mystery of consciousness; but it shared in reconciling a small minority of Englishmen to the mortality of their minds.

Another clergyman, Étienne Bonnot de Condillac, approached the problems of mind from a purely psychological side. Born at Grenoble (1714), he was educated at a Jesuit seminary in Paris, and was ordained a priest. Admitted to the salons of Mme. de Tencin and Mme. Geoffrin, he met Rousseau and Diderot, lost religious ardor, abandoned all sacerdotal functions, and gave himself to the game of ideas. He studied the historic systems of philosophy, and rejected them in a Traité des systèmes (1749), which voiced the spirit of the philosophes: all these proud structures of co-ordinated half-truths are fanciful proliferations from our fragmentary knowledge of the universe; it is better to examine a part of experience inductively than to reason deductively about the whole.

In an Essai sur l’origine des connaissances humaines (1746) Condillac had followed Locke’s analysis of mental operations; but in his most successful production, Traité des sensations (1754), he accepted a more radical view—that the “reflection” in which Locke had recognized a second source of ideas is itself only a combination of sensations, which are the sole source of all mental states. An external world exists, for our most basic sense, that of touch, encounters resistance; nevertheless, all that we know is our sensations and the ideas that they generate.

Condillac illustrated this proposition with a famous comparison. Perhaps he took it from Buffon, but he ascribed it to his late inspiratrice Mlle. Ferrand, who had left him an obliging legacy. He pictured a marble statue “organized internally like ourselves, but animated by a mind shorn of all ideas,”133 possessing only one sense, that of smell, and capable of distinguishing between pleasure and pain. He proposed to show how from the sensations of this statue all forms of thought could be derived. “Judgment, reflection, desires, passions, etc., are merely sensations variously transformed.”134 Attention is born with the first sensation. Judgment comes with the second, which begets comparison with the first. Memory is a past sensation revived by a present sensation or by another memory. Imagination is a memory vividly revived, or a group of memories projected or combined. Desire or aversion is the active memory of a pleasant or disagreeable sensation. Reflection is the alternation of memories and desires. Will is a strong desire accompanied by an assumption that the object is attainable. Personality, the ego, the self, does not exist at the outset; it takes form as the total collection of the individual’s memories and desires.135 In this way, from merely the sense of smell—or from any other one sense-nearly all operations of the mind can be deduced. Add four other senses, and the statue develops a complex mind.

All this was an interesting tour de force, and it made considerable noise among the intellectuals of Paris. But critics had no difficulty in showing that Condillac’s method was as deductive and hypothetical as anything in the systems of philosophy; that he quite ignored the problem of consciousness; and that he had not explained how the original sensitivity had arisen. A sensitive statue, even if it only smells, is no statue, unless it be that dignitary whom Turgenev described as posing as proudly as if he were his own monument raised by public subscription.

In 1767 Condillac was appointed tutor to the future Duke of Parma. He spent the next nine years in Italy, and composed for his pupil seventeen volumes which were published in 1769–73 as Cours d’études, or Course of Studies. These volumes are of a high order, but the two on history deserve a special salute because they included the history of ideas, manners, economic systems, morals, arts, sciences, amusements, roads—altogether a fuller record of “civilization” than Voltaire had given in the Essai sur les moeurs. In 1780, at the request of Prince Ignacy Potocki, Condillac drew up a Logique for the schools of Lithuania; this too was of exceptional excellence. In that year he died.

His influence survived for a century, appearing as late as 1870 in Taine’s De l’Intelligence. Condillac’s psychology was standard in the educational system established by the National Convention that governed France from 1792 to 1795. Anatomists like Vicq-d’Azyr, chemists like Lavoisier, astronomers like Laplace, biologists like Lamarck, alienists like Pinel, psychologists like Bonnet and Cabanis, acknowledged his lead. Pierre Jean Georges Cabanis, in 1796, described the brain as “a special organ whose particular function it is to produce thought, just as the stomach and the intestines have the special function of carrying on the work of digestion, and the liver that of filtering bile.”136 The philosophes who surrounded Condillac ignored his professions of faith in God, free will, and an immaterial, immortal soul; they claimed that a naturalistic, semimaterialistic, hedonistic philosophy logically followed from his reduction of all knowledge to sensation, and of all motives to pleasure and pain. Rousseau and Helvétius concluded that if the mind of man at birth is mere receptivity, education can mold intelligence and character with little regard to hereditary differences of mental capacity. Here was the psychological ground of many radical political philosophies.

The reaction against materialistic psychology came in France only after Napoleon had clipped the claws of the Revolution and had signed the Concordat of 1801 with the Church. It came earlier in Germany, where the antisensationist tradition of Leibniz was still strong. Men like Johann Nicolaus Tetens, professor at the University of Rostock, attacked the school of Condillac as mere theoreticians rather than scientists. All this talk of “vibrations” and “nerve fluid” was pure hypothesis; had anyone seen these things? Tetens argued that a scientific psychology would seek direct observation of mental processes; it would make introspection its major instrument, and would thereby build up a psychology on a truly inductive basis. It would soon find that the “laws of association” formulated by Hobbes, Locke, and Hartley do not correspond with our actual experience; that imagination often revives or combines ideas in quite a different order from that in which sensation gave them; and that links in the chain of association sometimes drop out in a very fanciful way. Desire seems to be the immanent reality of an organism, and hardly conforms to mechanical laws. Mind is an active, forming force, not a “blank paper” upon which sensation writes its will.

So the stage was set for Immanuel Kant.

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