Locke's intelligence was clear enough to perceive that these two ideas, spirit and matter, stand on a similar footing. Less lucid thinkers have boldly denied the existence of spirit while asserting that of matter. Locke's system would not allow him to believe that either conception depended on the nature of the mind itself. He therefore rejected the claims of substance as unequivocally as those of spirit, declaring it to be "only an uncertain supposition of we know not what, i. e., of something whereof we have no particular, distinct, positive idea, which we take to be the substratum or support of those ideas we know." Yet he inclines on the whole toward materialism. "We have," he says, "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 system of matter, fitly disposed, a power to perceive and think, or else joined and fixed to matter so disposed a thinking immaterial substance, it being, in respect of our notions, not much more remote from our comprehension to conceive that God can, if he pleases, superadd to matter a faculty of thinking, than that he should superadd to it another substance, with a faculty of thinking; since we know not wherein thinking consists, nor to what sort of substances the Almighty has been pleased to give that power, which cannot be in any created being, but merely by the good pleasure and power of the Creator."... "All the great ends of morality and religion," he adds, "are well secured without philosophical proof of the soul's immateriality." As to our knowledge "of the actual existence of things, we have an intuitive knowledge of our own existence, and a demonstrative knowledge of the existence of God; of the existence of anything else, we have no other but a sensitive knowledge, which extends not beyond the objects present to our senses."[Footnote: Is not an intuitive knowledge suspiciously like an innate idea? Locke's _Works_, i. 38, 39, 72, 82, 137, 145, 231; ii. 10, 11, 21, 331, 360, 372 (Book i. ch. 3, 4, Book ii. ch. 1, 10, 11, 20, 23, Book iv. ch. 3).]