  Second, there is what can best be described as a genuinely idealist strand of Leibniz's thought. That is, if idealism is the thesis that the only things that truly exist are minds and their ideas, then Leibniz clearly espouses this doctrine. Here the operative idea is that bodies, and in particular the bodies associated with particular minds, are intentional objects – though they result from or are grounded in monads. This is what Leibniz is getting at in the following passage from another letter to De Volder: “considering the matter carefully, we must say that there is nothing in things but simple substances, and in them, perception and appetition. Moreover, matter and motion are not substances or things as much as they are the phenomena of perceivers, the reality of which is situated in the harmony of the perceivers with themselves (at different times) and with other perceivers” (G II 270/AG 181). Thus, the only real things are simple substances; the bodies that we perceive in motion around us are phenomena and not themselves substances, though they are grounded ultimately in simple substances or monads. Furthermore, the bodies of the natural world ought be considered intentional objects in that they are objects about which we have certain beliefs. This is what Leibniz means in saying that they have reality insofar as there is a harmony between perceivers or between the same perceivers' beliefs or perceptions at different times. In other words, one's body or even a stone is real because it is an object of perception that fits into an account of the world that is both coherent from the point of view of the single perceiver and in harmony with the perceptions of other minds.