He was born at Grenoble of a legal family, and, like his elder brother, the well-known political writer, abbé de Mably, took holy orders (1733-1740) at Saint-Sulpice in Paris and became Abbot of Mureau. In both cases the profession was hardly more than nominal, and Condillac's whole life, with the exception of an interval as tutor at the court of Parma, was devoted to speculation. His works are Essai sur l'origine des connaissances humaines (1746), Traité des systèmes (1749), Traité des sensations (1754), Traité des animaux (1755), a comprehensive Cours d'études (1767-1773) in 13 vols., written for the young Duke Ferdinand of Parma, a grandson of Louis XV, Le Commerce et le gouvernement, considérés relativement l'un a l'autre (1776), and two posthumous works, Logique (1781) and the unfinished Langue des calculs (1798).

In Paris he came much into contact with the circle of Diderot. A friendship with Rousseau, which lasted in some measure to the end, may have been due in the first instance to the fact that Rousseau had been domestic tutor in the family of Condillac's elder brother, Jean Bonnot, known as Monsieur de Mably, at Lyon. Thanks to his natural caution and reserve, Condillac's relations with unorthodox philosophers did not injure his career; and he justified abundantly the choice of the French court in sending him to Parma to educate the orphan duke, then a child of seven years.

In 1768, on his return from Italy, he was elected to the Académie française; contrary to the popular idea that he attended only one meeting, he was a frequent attender until two years before his death. He spent his later years in retirement at Flux, a small property which he had purchased near Beaugency, and died there on 3 August 1780.

Condillac is important both as a psychologist and as having established systematically in France the principles of Locke, whom Voltaire had lately made fashionable. In setting forth his empirical sensationism, Condillac shows many of the best qualities of his age and nation, lucidity, brevity, moderation and an earnest striving after logical method.

His first book, the Essai sur l'origine des connaissances humaines, keeps close to his English master. He accepts with some indecision Locke's deduction of our knowledge from two sources, sensation and reflection, and uses as his main principle of explanation the association of ideas. His next book, the Traité des systèmes, is a vigorous criticism of those modern systems which are based upon abstract principles or upon unsound hypotheses. His polemic, which is inspired throughout by Locke, is directed against the innate ideas of the Cartesians, Malebranche's faculty-psychology, Leibniz's monadism and preestablished harmony, and, above all, against the conception of substance set forth in the first part of the Ethics of Spinoza.

By far the most important of his works is the Traité des sensations, in which he emancipates himself from the tutelage of Locke and treats psychology in his own characteristic way. He had been led, he tells us, partly by the criticism of a talented lady, Mademoiselle Ferrand, to question Locke's doctrine that the senses give us intuitive knowledge of objects, that the eye, for example, naturally judges shapes, sizes, positions and distances. His discussions with the lady had convinced him that to clear up such questions it was necessary to study our senses separately, to distinguish precisely what ideas we owe to each sense, to observe how the senses are trained, and how one sense aids another. The result, he was confident, would show that all human faculty and knowledge are transformed sensation only, to the exclusion of any other principle, such as reflection. The plan of the book is that the author imagines a statue organized inwardly like a man, animated by a soul which has never received an idea, into which no sense-impression has ever penetrated. He then unlocks its senses one by one, beginning with smell, as the sense that contributes least to human knowledge. At its first experience of smell, the consciousness of the statue is entirely occupied by it; and this occupancy of consciousness is attention. The statue's smell-experience will produce pleasure or pain; and pleasure and pain will thenceforward be the master-principle which, determining all the operations of its mind, will raise it by degrees to all the knowledge of which it is capable. The next stage is memory, which is the lingering impression of the smell experience upon the attention: "memory is nothing more than a mode of feeling." From memory springs comparison: the statue experiences the smell, say, of a rose, while remembering that of a carnation; and "comparison is nothing more than giving one's attention to two things simultaneously." And "as soon as the statue has comparison it has judgment." Comparisons and judgments become habitual, are stored in the mind and formed into series, and thus arises the powerful principle of the association of ideas. From comparison of past and present experiences in respect of their pleasure-giving quality arises desire; it is desire that determines the operation of our faculties, stimulates the memory and imagination, and gives rise to the passions. The passions, also, are nothing but sensation transformed. These indications will suffice to show the general course of the argument in the first section of the Traité des sensations. To show the thoroughness of the treatment it will be enough to quote the headings of the chief remaining chapters: "Of the Ideas of a Man limited to the Sense of Smell," "Of a Man limited to the Sense of Hearing," "Of Smell and Hearing combined," "Of Taste by itself, and of Taste combined with Smell and Hearing," "Of a Man limited to the Sense of Sight." In the second section of the treatise Condillac invests his statue with the sense of touch, which first informs it of the existence of external objects. In a very careful and elaborate analysis, he distinguishes the various elements in our tactile experiences - the touching of one's own body, the touching of objects other than one's own body, the experience of movement, the exploration of surfaces by the hands: he traces the growth of the statue's perceptions of extension, distance and shape. The third section deals with the combination of touch with the other senses. The fourth section deals with the desires, activities and ideas of an isolated man who enjoys possession of all the senses; and ends with observations on a "wild boy" who was found living among bears in the forests of Lithuania. The conclusion of the whole work is that in the natural order of things everything has its source in sensation, and yet that this source is not equally abundant in all men; men differ greatly in the degree of vividness with which they feel; and, finally, that man is nothing but what he has acquired; all innate faculties and ideas are to be swept away. The last dictum suggests the difference that has been made to this manner of psychologizing by modern theories of evolution and heredity.

Condillac's work on politics and history, contained, for the most part, in his Cours d' études, offers few features of interest, except so far as it illustrates his close affinity to English thought: he had not the warmth and imagination to make a good historian. In logic, on which he wrote extensively, he is far less successful than in psychology. He enlarges with much iteration, but with few concrete examples, upon the supremacy of the analytic method; argues that reasoning consists in the substitution of one proposition for another which is identical with it; and lays it down that science is the same thing as a well-constructed language, a proposition which in his Langue des calculs he tries to prove by the example of arithmetic. His logic has in fact the good and bad points that we might expect to find in a sensationist who knows no science but mathematics. He rejects the medieval apparatus of the syllogism; but is precluded by his standpoint from understanding the active, spiritual character of thought; nor had he that interest in natural science and appreciation of inductive reasoning which form the chief merit of JS Mill. It is obvious enough that Condillac's anti-spiritual psychology, with its explanation of personality as an aggregate of sensations, leads straight to atheism and determinism. There is, however, no reason to question the sincerity with which he repudiates both these consequences. What he says upon religion is always in harmony with his profession; and he vindicated the freedom of the will in a dissertation that has very little in common with the Traité des sensations to which it is appended. The common reproach of materialism should certainly not be made against him. He always asserts the substantive reality of the soul; and in the opening words of his Essai, "Whether we rise to heaven, or descend to the abyss, we never get outside ourselves -- it is always our own thoughts that we perceive," we have the subjectivist principle that forms the starting-point of Berkeley.

Condillac saw language as the vehicle by which senses and emotions were transformed into higher mental faculties. He believed that the structure of language reflects the structure of thought and compared ideas to the sounds of a harpsichord. His theories had a major effect on the development of linguistics. Condillac promoted "sensationalism," a theory that says all knowledge comes from the senses and that there are no innate ideas. Condillac was not a naive sensationalist but put forward an expressionist theory of linguistic creation that anticipates the prime features of German theorist the thought of Johann Gottfried Herder (1744-1803) later thoughts about language.

Condillac's 'Le Commerce et le Gouvernement' (1776) attempted to place economics in a coherent logical framework. He was a friend of friend François Quesnay, leader of the Physiocrats. Much of Condillac's work reflected mainstream Physiocrats, particularly his analysis of the structure of taxation and proposals for the revival of the economy, but he also proposed another line of argument, claiming that producers work to obtain utility. Most physiocrats rejected utility and the idea was ignored until his 'rediscovery' by Stanley Jevons and Carl Menger in 1871.

In his theory of "vrai prix" [true price] Condillac proposed a theory of human history divided into two phases: progress and decline. Progress is marked by a rational development and use of resources; decline is precipitated by bad behavior from the upper classes that then trickles down to the workers, encouraging excess, luxury, and false prices that harm the masses. Condillac saw the remedy to this as "vrai prix," a true price created by the unimpeded interaction of supply and demand, to be achieved by complete deregulation. People would be taught to work toward their best interest in an open market through a reshaping of their perceptions. By advocating of a free market economy in contrast to the prevailing contemporary policy of state control in France, Condillac influenced classical liberal economics.

Condillac's Histoire ancienne and Histoire moderne (1758-1767) demonstrated how the experience and observation of the past aided man. History was not a mere retelling of the past, but a source of information and inspiration as well. Reason and critical thinking can improve man's lot and destroy superstition and fanaticism. History thus served as a moral, political, and philosophical textbook which taught man to live better. Thus the two histories present the basic program of the Enlightenment in crystallized form.