Customer Reviews

Jean d'Alembert: Science and the Enlightenment (Classics in the History and Philosophy of Science,)

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This book furnishes us with an interesting opportunity to highlight an important instance of the fallacy of putting the cart before the horse.

Perhaps the cleanest illustration is provided by a discussion of Newton's "marvellous" (p. 183) proof of the law of equal areas. In this "marvellous" proof, "the gravitational force is assumed to consist of [discrete] periodic blows driving the planet towards the sun" (p. 183). Hankins rationalises this assumption as follows: "If Newton believed in the existence of perfectly hard bodies (and he apparently did), it is understandable why he made forces proportional to finite changes in momentum" (p. 183; thus the assumption in the proof of the law of equal areas would be true if gravity was caused by an 'aether' of such bodies).

I say that Hankins gets things entirely backwards when he tries to rationalise "marvellous proofs" in terms of philosophical or metaphysical doctrines (such as the existence of perfectly hard bodies). The arrow of justification goes in the opposite direction: we adhere to whatever philosophical or metaphysical principles that will enable us to produce "marvellous proofs."

To see that a "marvellous proof" is the horse and metaphysics the cart in the case of d'Alembert, one need only understand the character of the "physique de salon" (p. 97) in which he was engaged.

"The salons, the opera, the academies, and the daily round of conversations with his friends were what sustained his interest. ... many letters testify to his ability to charm an audience. [E.g.:] '[D'Alembert's conversation] offers all that can instruct and refresh the mind. He lends himself with as much ease and willingness to whatever topic is most pleasing and brings to it his good-nature and naiveté with an almost inexhaustible source of ideas, anecdotes and curious recollections. ...' The importance of such an endowment should not be underestimated in a society where the bon mot and the witty epigram were frequently the measure on one's worth." (pp. 15-16)

If you want to "charm an audience" in this way, the unit of progress is a "bon mot," i.e., a "marvellous proof." Shifting metaphysical assumptions is not a problem; it merely reflects your ability to "lend yourself to whatever topic is most pleasing."

But even with this evidence in front of his eyes, poor old Hankins clings to the notion that these Parisian "philosophes" must share a philosophical core. It is amusing to watch Hankins try to get all these horses to follow his cart. For instance we read:

"d'Alembert fought consistently to further the cause of philosophie. The battle was real enough and so was d'Alembert's vigorous involvement in it, but the cause for which the philosophes expended so much energy is not so easy to describe. The attempt to define a philosophe or state his creed usually leads first to embarrassment and then to paradox. ... Unfortunately the philosophes were in frequent disagreement, changed their minds, and ... were not at all clear about some of the important ideas they professed. As a result, we can find philosophes who argued both sides of almost any question, and the paradoxes can be multiplied without limit." (pp. 12-13)

As we have seen, the "embarrassment" and alleged "paradoxes" is merely the result of looking for the common denominator in the wrong sphere---that of philosophical premises rather than that of "marvellous proofs."

To see the same point demonstrated again, consider, if you like, how d'Alembert first got involved in this business of "fermentation of minds" (p. 70), as he himself called it.

In his youth, d'Alembert became friends with Diderot, Condillac and Rousseau "in the bohemian café society of Paris" (p. 66). "One wonders how this group of four relatively unknown intellectuals ever came together in a city the size of Paris; or what critical combination of talents carried them all to fame. Again one searches in vain for a common denominator, either social, political, or intellectual, that would obviously have united them in a common cause. The Abbé Condillac, not devout, but certainly not anti-religious, was a philosopher in the traditional sense. He read his predecessors with care and exponded his ideas on the theory of knowledge, scientific method, etc., in well-organized, logical treatises, every one bearing his name on the title page. Diderot usually published clandestinely, saw his books condemned, visited the dungeon at Vincennes, and continued to produce books full of philosophical insight, vigorous prose, dangerous propaganda, and general disorder. Rousseau was unique. A Genevan vagabond, who was probably attracted to Diderot and d'Alembert by a common interest in music, he proved to have the greatest fund of sensibilité and the best romantic prose of any Enlightenment author. These were the men who turned d'Alembert's head to philosophy." (p. 27)

I say: "search in vain" no more. It was their appreciation of "marvellous proofs" that united "this little philosophical band" (p. 27).