Say was born in Lyons.
His father, Jean-Etienne Etienne Say, was of Protestant family which had moved from Nîmes, to Geneva for some time in consequence of the revocation of the Edict of Nantes. Say was intended to follow a commercial career, and was sent, with his brother Horace, to England: here he lived first in Croydon, in the house of a merchant, to whom he acted as clerk, and afterwards in London, where he was in the service of another employer. When, on the death of the latter, he returned to France, he was employed in the office of a life assurance company directed by Étienne Clavière.
Say's first literary attempt was a pamphlet on the liberty of the press, published in 1789. He later worked under Mirabeau on the Courrier de Provence. In 1792 he took part as a volunteer in the campaign of Champagne; in 1793 he assumed, in conformity with the Revolutionary fashion, the pre-name of Atticus, and became secretary to Clavière, then finance minister.
In 1793 Say married Mlle Deloche, daughter of a former lawyer. From 1794 to 1800 Say edited a periodical entitled La Decade philosophique, litteraire, et politique, in which he expounded the doctrines of Adam Smith. He had by this time established his reputation as a publicist, and, when the consular government was established in 1799, he was selected as one of the hundred members of the tribunate, resigning the direction of the Decade.
In 1800 he published in Olbie, ou essai sur les moyens de reformer les moeurs d'une nation. In 1803 appeared Say's principal work, the Traite d'economie politique. In 1804, having shown his unwillingness to sacrifice his convictions for the purpose of furthering the designs of Napoleon, he was removed from the office of tribune. He then turned to industrial pursuits, and, having made himself acquainted with the processes of the cotton manufacture, founded at Auchy, in the Pas de Calais, a spinning-mill which employed four or five hundred persons, principally women and children. He devoted his leisure to the improvement of his economic treatise, which had for some time been out of print, but which the censorship did not permit him to republish.
In 1814 he "availed himself" (to use his own words) of the sort of liberty arising from the entrance of the allied powers into France to bring out a second edition of the work, dedicated to the emperor Alexander I of Russia, who had professed himself his pupil. In the same year the French government sent him to study the economic condition of Great Britain. The results of his observations appeared in A tract de l'Angleterre et des Anglais.
A third edition of the Traite appeared in 1817. A chair of industrial economy was founded for him in 1819 at the Conservatoire des Arts et Metiers. In 1831 he was made professor of political economy at the College de France. Say in 1828–1830 published his Cours complet d'economie politique pratique.
In his later years Say became subject to attacks of nervous apoplexy. He lost his wife in January 1830; and from that time his health constantly declined.
When the revolution of that year broke out, he was named a member of the council-general of the department of the Seine, but found it necessary to resign.
He died in Paris on November 15, 1832.
He is well known for Say's Law (or Say's Law of Markets), often summarised as
He argued that production and sale of goods in an economy automatically produces an income for the producers of the same value, as production is determined by the supply of goods rather than demand. Unemployment of men, land or other resources would not be possible unless it were by choice, or due to some kind of restraint on trade.
He was also among the first to argue that money was neutral in its effect on the economy. Money is not desired for its own
Say's ideas helped to inspire neoclassical economics which arose later in the 19th century. He wrote Traite d’Economique Politique.
As an interesting conjecture, Say's Law may have culled from Ecclesiastes 5:10 — "As goods increase, so do those who consume them. And what benefit are they to the owner except to feast his eyes on them?" (NIV)
"To encourage whale-hunting, the English government prohibits vegetable oils which we burn in France in draught-lamps. What results from this? That one of these lamps, which costs a Frenchmen 60 francs per year, costs an Englishman 150 francs. The intention, some say, is to support the navy and to multiply the number of sailors, that each lamp nozzle costs Englishmen 90 more franks than in France. In this case, it is to multiply the number of sailors by the means of a trade that generates losses: it would be better to multiply them by a lucrative trade."
"A hard working laborer, I was told, fancied working by candlelight. He had calculated that, during his vigil, he burned a 4-penny candle, earning 8 pennies by his work. A tax on tallows and another on the manufacture of the candles increased by 5 pennies the cost of his luminary, which became thus more expensive than the value of the product that it could shed light upon. From then on, as soon as night fell, the workman remained idle; he lost the 4 pennies which his work could obtain him, and without the tax service perceiving anything out of this production. Such a loss must be multiplied by the number of the workmen in a city and by the number of the days of the year."
Samuel Hollander - Jean-Baptiste Say and the Classical Canon in Economics: the British Connection in French Classicism (London and New York: Routledge), 2005, xiii + 322, ISBN 0-415-32338-X
Thomas Sowell - Say's Law: An Historical Analysis (Princeton University Press), 1973, 254, ISBN 0-691-04166-0