The picture of a universe of infinitely many wholly unrelated substances is at least as hard to understand as the monism of Spinoza, and far less easy to reconcile with appearances.

The seclusion of Spinoza’s life was necessitated by intense labour and intellectual discipline, and his frugality expressed independence of spirit rather than meanness or self-concern. The strength of Spinoza’s social feelings, and his Aristotelian emphasis on friendship as a necessary human good, are abundantly shown in the Ethics.

Religious quarrels,’ he added, ‘do not arise so much from ardent zeal for religion, as from men’s various dispositions and love of contradiction, which causes them habitually to distort and condemn everything, however rightly it may have been said.

The letters between the two philosophers were cordial, although Spinoza at first distrusted Leibniz, who in turn referred to him privately as ‘a Jew expelled from the synagogue for his monstrous opinions’. Since the fundamental assumptions behind their two systems are profoundly similar, it is perhaps not surprising that the two philosophers – whose conclusions are wholly opposed – should have treated each other with a certain caution.