THE THINKING PROCESS
We know that there are two ways of being conscious of objects, which we distinguish as perceiving and thinking: or, abstractly, as perception and thought. The attempt to define these terms leads to mere circumlocutions, but the processes to which they refer can be pointed out in concrete experiences. I perceive the vase of roses now on the table before me, in full daylight. An hour from now, when I am in another room, I may think of them: in this particular case, I may imagine them. The different types of thought--imagination, memory, conception--have been discussed already in Chapter VIII.
For the detailed understanding of thought; for the analysis of the conditions under which it occurs, and the ascertaining of its laws, it is necessary to reduce it to a psychobiological basis, just as has been done for perception. The empirical similarities between thought and perception, and the dependence of the second upon the first, as already discussed, indicate that the basis of the two processes is essentially the same: that thought, like perception, is intrinsically a reaction. The principle of parsimony, moreover, would necessitate our considering this hypothesis, and determining how far it fits the known facts and promotes further investigation.
Reaction involves stimulation. Every reaction begins in the activity of receptors, which must be stimulated in some definite way. We must seek in the body therefore, for the neural mechanism capable of sustaining a thought reaction, and seek for the probable stimulus. At the outset, we must exclude the receptors of the so-called special senses: vision, audition, gustation, olfaction, and the dermal senses. In the first place, the functioning of these initiates perception: in the second place, thought, even thought of objects which appeal perceptually to these senses, may