At first sight it may appear (but why it should can only become clear later) that here we have two kinds of worlds, worlds built of different materials; a mental world and a physical world. The mental world in fact is liable to be imagined as gaseous, or rather, ethereal. But let me remind you here of the queer role which the gaseous and the ethereal play in philosophy, ‒ ‒ ‒ when we perceive that a substantive is not used as what in general we should call the name of an object, and when therefore we can't help saying to ourselves that it is the name of an ethereal object. I mean, we already know the idea of “ethereal objects” as a subterfuge, when we are embarrassed about the grammar of certain words¤
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and when all we know is that they are not used as names for material objects. This is a hint as to how the problem of the two materials, mind and matter, is going to dissolve.