The topic is freedom. Schmaltz notes that Malebranche holds that interior sentiment suffices to demonstrate our freedom. He then cites Leibniz's magnetic needle passage in the Theodicy and a little later says,
It msut be said, however, that it is difficult in light of Leibniz's critical remarks to accept the introspectionist proof of freedom common to Descartes and Malebranche. Leibniz's example of the magnetic needle effectively brings home the point that our actions coudl appear to us to be free and independent and yet still be determined by causes of which we are ignorant. Even if it is not intelligible to suppose that we do not have a certain sensation when there is the appearance of this sensation in us, certainly it is intelligible to suppose that we are not free when there is the appearance of freedom in us. Malebranche's claim to Arnauld that our inner sentiment of freedom yields certain knowledge of the existence of our freedom in just the same way that our inner sentiment of pain yields a certain knowledge of the existence of pain simply lacks persuasive force.
I'm inclined to think that Malebranche is on much stronger ground, on this point at least, than Schmaltz suggests. First, Malebranche's occasionalism gets in the way of the objection. The whole point of occasionalism is that there is no possible determining cause except God. This means that the only potential threat to Malebranche's {occasionalism + interior sentiment of freedom} position is theological determinism. However:
1. (As Schmaltz goes on to note) Malebranche has a subsidiary argument that blocks theological determinism, based on the impossibility of God being the author of our sin.
2. Further, (here I am being more speculative) Malebranche does attribute more to interior sentiment than the bare passing of what goes on in the soul; e.g., it is by interior sentiment that we know the guidance of Reason, and it is by interior sentiment that we know that God wills Order, and it plays a role in Adam's understanding of occasional causation. So it isn't implausible to interpret Malebranche as thinking interior sentiment can handle any deterministic threat on its own. How, of course, would be a trickier question (although not necessarily unanswerable); but, given what Malebranche ascribes to interior sentiment elsewhere, a bit more is needed on this point.
