In this chapter, Locke maintains that there is no more difficulty, if indeed so much, in the notion of immaterial spirit as of body. "Our idea of Body, as I think, is an extended solid substance, capable of communicating motion by impulse; and our idea of our Soul, as an immaterial Spirit, is of a substance that thinks, and has a power of exciting motion in body by Will or Thought." (§ 22.) Now, it is "no more a contradiction that Thinking should exist separate and independent from Solidity, than it is a contradiction that Solidity should exist separate and independent from Thinking, they being both but simple ideas independent one from another. And, having as clear and distinct ideas in us of Thinking as of Solidity, I know not why we may not as well allow a thinking thing without solidity, that is immaterial, to exist, as a solid thing without thinking, that is matter, to exist; especially since it is no harder to conceive how Thinking should exist without Matter, than how Matter should think." (§ 32.) In the Fourth Book (ch. iii., § 6), however, he gave great scandal by suggesting the possibility that Matter might think, that it was not much more repugnant to our conceptions that God might, if he pleased, "superadd to Matter a Faculty of Thinking, than that he should superadd to it another substance with a faculty of thinking." At the same time, he regarded it as no less than a contradiction to suppose that Matter, "which is evidently in its own nature void of sense and thought," should be the "eternal first thinking Being," or God Himself; and, in his First Letter to the Bishop of Worcester, he grants that _in us_ (as distinguished from the lower animals) it is in the highest degree probable that the "thinking substance" is immaterial. Materialism, therefore, as ordinarily understood, is certainly no part of Locke's system.