The second pair of topics in the Leibniz’s preface to his book on Locke concern bodies or matter—although, in the case of the second, in relation to thought.
• The two topics tend to run into one another, but the focus of the first is the difference between Leibniz’s conception of matter and two contrary views, both of which he finds in Locke: (i) an account of the material world in terms of atoms and the void and (ii) an acceptance of attraction at a distance (as found in Newton’s conception of gravity). In both respects, Leibniz holds views in keeping with Descartes and, in the latter case, with the point of view of 17th century science generally. (Even Newton wrote, at points, as though the idea of gravity was suspect and something calling for further explanation.)
• The tie between this first topic and the second one is stated by Leibniz on p. 61: just as Locke seems ready to grant to matter the unintelligible power to attract other matter at arbitrary distances, he seems ready to entertain the possibility of something equally unintelligible, matter that thinks. The topic of thinking matter arose in Locke incidentally. As an example of the limits of our knowledge, Locke says we cannot know whether God has the power to make matter think. In order to maintain that we cannot know this to be impossible, he claims that there is nothing contradictory about the idea.
Leibniz’s repeated reference to “occult qualities” when criticizing Locke on both points suggests that he sees Locke as reverting to views found in late Renaissance combinations of scholastic views with neo-platonism, a constellation of ideas that scientists of the 17th century had tried to move beyond. For example, since the way magnetism operates is not open to view, it would have seemed natural around 1600 to see it as a specific hidden or “occult” power or “virtue” of lodestone attributable to the “substantial form” of that material. And, wishing to counter such a view, Descartes had offered a mechanical explanation (via the emission of particles with helical groves).