Have lofty sentiments, he said, and your manner of writing will be firm and noble.[100] Yet he did not ignore the other side and half of the truth, which is expressed in the saying of another important writer of that day--By taking trouble to speak with precision, one gains the habit of thinking rightly (_Condillac_).
Like so many others to whom literature owes much, D'Alembert was all his life fighting against bad health.

Like Voltaire and Rousseau, he was born dying, and he remained delicate and valetudinarian to the end.

He had the mental infirmities belonging to his temperament.

He was restless, impatient, mobile, susceptible of irritation.

When the young Mademoiselle Phlipon, in after years famous as wife of the virtuous Roland, was taken to a sitting of the Academy, she was curious to see the author of the Preliminary Discourse to the Encyclopaedia, but his small face and sharp thin voice made her reflect with some disappointment, that the writings of a philosopher are better to know than his mask.[101] In everything except zeal for light and emancipation, D'Alembert was the opposite of Diderot.