They were both "Immaterialists," because they both discerned the radical difference between mental and material phenomena, and because they both admitted the reasonableness of ascribing them, respectively, to a _distinct substance_.

But they were not convinced by the more metaphysical arguments of those who professed to show that none of the phenomena of "mind" could possibly be exhibited by matter, or, at least, they declined to take that ground.

That Locke was an Immaterialist is evident from many passages in his writings.

"By putting together," he says, "the ideas of thinking, perceiving, liberty and power of moving themselves and other things, we have as clear a perception and notion of immaterial substances as we have of material.
For putting together the ideas of thinking and willing, &c., joined to _substance_, of which we have no distinct idea, we have the idea of an immaterial spirit; and by putting together the ideas of coherent solid parts and a power of being moved, joined with _substance_, of which likewise we have no positive idea, we have the idea of matter: the one is as clear and distinct an idea as the other."[165] But notwithstanding this explicit statement, he demurred to the doctrine of those who maintained that the power of thinking could not possibly be superadded to matter, and this because he deemed it presumptuous to set limits to the Divine omnipotence, or to pronounce any judgment on a question of that kind.

"We have the ideas of matter and thinking, but possibly shall never be able to know whether any mere material being thinks or no; it being impossible for us, by the contemplation of our own ideas, without Revelation, to discover whether Omnipotency has not given to some systems of matter, fitly disposed, a power to perceive and think....