Hylas is still not ready to give up. He accepts that God is the ultimate cause of all our ideas, but wonders, could there not still be such a thing as matter? He believes that God may cause our ideas through the use of matter. This returns us to the discussion of whether we can infer the existence of mind-independent material objects. Hylas is now raising the final possibility: that we can infer matter as the cause of our ideas. He will raise this same possibility in several guises before he finally gives it up.
The idea that matter causes our ideas is familiar. Through the motion of particles, goes the usual theory, matter somehow stimulates us and gives rise to our ideas. Philonous, of course, does not put very much stock in this theory. Motion, he points out, is an idea, as we have already established. Ideas, though, are passive and inert and so cannot cause anything. The only thing in the world that is active is will, so will is the only causal agent. Only volition can act as cause. So matter cannot be the cause of our ideas.
But perhaps, Hylas presses, God uses matter as his instrument, in order to cause ideas in us. Philonous likes this idea even less than the previous one. First of all, he asks, what could these instruments be like, since we know that they cannot have any sensible qualities? More importantly, though, why on earth would God need an instrument? We only need an instrument for something if we cannot do it on our own, through a sheer act of the will, but God can do everything by a sheer act of the will. He's omnipotent. So God would never need an instrument.
Hylas is becoming increasingly desperate, and he suggests that matter is an "occasion", by which he means "an inactive, unthinking being, at the presence whereof God excites ideas in our minds". This would explain the order and regularity of our sensations — why we always have certain sensations followed by others, like the sensation of seeing fire followed by the sensation of feeling heat. Philonous points out that we already have sufficient explanation for this phenomenon in the fact of God's wisdom — this is just how He arranged things. And it is insulting to God to insinuate that he needs extra help from inert objects.
Hylas has one last possibility up his sleeve: matter is not a substratum, or an archetype, or a cause, or an instrument, or an occasion, but, rather, it is just something totally unknown, the abstract general idea of entity. In response to this suggestion, Philonous points out that this entity, whatever it is, cannot exist anywhere, because if it exists in space then it must exist in the mind since space or extension only exists in the mind. Then he asks whether Hylas has any positive notion of this entity at all, and Hylas admits he that he does not. Philonous concludes that this notion is, therefore, meaningless and empty, just as are all abstract general ideas.
Exhausted and defeated, Hylas admits that he has no way to answer any of Philonous' arguments. He stubbornly maintains, however, that he is unconvinced of idealism in his gut. Philonous counters that the only reason Hylas remains unconvinced, is that he is prejudiced against idealism. This does not indicate any weakness on the part of the arguments, but only the strength of Hylas' brainwashing.