ABSTRACT
WE have seen that sensation is the ultimate source of a very large number of the concrete processes that go to make up our mental life. Everything that we meet with in our world of ideas is derived in the last resort from sensations, and ideas are the raw material of all the higher mental activities. It may be questioned whether the stream of thought could not continue without any reinforcement from the outside world; but this at least is certain, that it has its source in sensibility, and that sensibility does perpetually interfere to determine its direction. In this way our investigation of sensation leads on directly to the consideration of a second and very important psychological problem,—the problem of the composition of ideas from the sensational elements that enter into them in so great number and variety.
