La langue des calculs, ouvrage posthume et élémentaire, imprimé sur les manuscrits autographes de l'auteur; Dans lequel des observations, faites sur les commencemens et les progrès de cette langue, démontrent les vices des langues vulgaires, et font voir comment on pourroit, dans toutes les sciences, réduire l'art de raissonerà une langue bien faite.

Paris, Charles Houel, an VI de la République (=1798). 8vo. Recent simple brown half cloth w. gilt title to spine. Uncut. Title-page w. large damp-stain, next few leaves w. a bit of soiling to upper corner. Occasinal brownspotting. Every gathering extended and re-inforced at hinge, probably in order to make the book open to its full extent. (2), 484, (1, -errata) pp.

The true first edition of this posthumously published major treatise, Condillac's final main work, which proved to be one of his most important and influential ones.

The work was originally published both separately, as it is here, with its own errata-leaf and title-page without mentioning of volume number for the Oeuvres, and as the final volume of his "Oeuvres philosophiques".

Having realized that other philosophers' accounts of knowledge had failed because they focused on the essences instead of the origins, Condillac, in all of his major treatises, set out to define moral and metaphysical problems as precisely as one can define the problems of geometry, and the approach that would enable this would be analytic. In the same stroke he would correct Locke's mistake of "Internal sense", the distinction between the process of sensation and of reflection. "His instrument was a highly original theory of language as the analyst of experience. It is by the mind's capacity to invent and manipulate symbols of uniform and determinate significance that it passes from sensation to reflection and communication and hence to effective knowledge... By identifying the operations of language as the cause of intellectual functions, Condillac intended to be making the kind of statement Newton had made when he identified gravity as the cause of planetary motion - an exact and verifiable generalization of phenomenal effects. " (D.S.B. III:381).

It is in his last major work that Condillac deals most thoroughly with the analysis of language and the language of algebra. Algebra is the language of mathematics, and it is the only language that is well done ("bien faite"), nothing in this language is arbitrary; the analogies of this language are always precise and lead on to new sensible expressions; in this language the purpose is not to learn to speak like others, the purpose is to speak in the greater analogy in order to reach a greater precision. Algebra, the language of mathematics, is a language of analogies. Analogy, which constitute this language, also constitutes the methods. "L'analogie: viola donc à quoi se réduit tout l'art de raisonner, comme tout l'art de parler; et dans ce seul mot, nous voyons comment nous pouvons nous instruire des découvertes des autres, et comment nous en pouvons faire nous-mêmes."(= "The analogy: now, this is what the entire art of reasoning as well as the entire art of talking can be reduced to; and with this single word we see how we can guide the discoveries of others, and how we can do them ourselves. [own translation]" (p. 7). And thus, the objective of this work is to see how it will be possible to give to other sciences the same exactness as that which we otherwise believe exclusively to be a part of mathematics, namely the exactness of the language of algebra.

"It was through his last works -"La logique" and, especially, "La langue des calculs"- that Condillac exercised the most decisive influence on the philosophical taste of the generation of scientists immediately following his own. Therein, like his predecessors in the rationalist tradition, he looked to mathematics as the exemplar of knowledge. He parted company with them, however, in developing the preference he had expressed in his early work for the analytic over the synthetic mode of reasoning." (D.S.B.; III:382). Algebra, seen as both a language and as the method of analysis, in comparison to the inaccurate instrument that is ordinary language would reveal to Condillac what is the difference between the problems of science and those of society, the moral and metaphysical ones. "And in that comparison Condillac's philosophy entered into the reforming mission of the Enlightenment, the central imperative of the rationalism then having been to reduce the imperfections of human arrangements by approximating them to the natural and to educate the human understanding in the grammar of nature. In Franceat least, the congruence of Condillac's philosophy of science with the broader commitments of progressive culture recommended it so scientists themselves as the most authoritative reading of Newtonian methodology... The terminology and symbolism of the modern science of chemistry are examples still alive in science of the practicality of this program." (D.S.B., III:382).

Condillac's philosophy of science was considered the most authoritative reading of Newtonian methodology. Among many others Lavoicier and other protagonists of the chemical revolution were influenced by his reform of nomenclature, as were and are botanists, zoologists and geometrics by his scientific explanations. His psychological empiricism is now considered the first positivist account of science.

Condillac was one of the greatest French philosophers of the Enlightenment. He was friends with Rousseau and Diderot and was a forerunner in the junction between epistemology and philosophy, which was inspired by Locke and Newton, as the two sciences almost merged into one in this period. "Condillac contibuted to the synthesis more decisively than did any other writer." (D.S.B. III:380).

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