CHAPTER XVII

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SENSATION.

After inner perception, outer perception! The next three chapters will treat of the processes by which we cognize at all times the present world of space and the material things which it contains. And first, of the process called Sensation.

SENSATION AND PERCEPTION DISTINGUISHED.

_The words Sensation and Perception_ do not carry very definitely discriminated meanings in popular speech, and in Psychology also their meanings run into each other. Both of them name processes in which we cognize an objective world; both (under normal conditions) need the stimulation of incoming nerves ere they can occur; Perception always involves Sensation as a portion of itself; and Sensation in turn never takes place in adult life without Perception also being there. They are therefore names for different cognitive _functions_, not for different sorts of mental _fact_. The nearer the object cognized comes to being a simple quality like 'hot,' 'cold,' 'red,' 'noise,' 'pain,' apprehended irrelatively to other things, the more the state of mind approaches pure sensation. The fuller of relations the object is, on the contrary; the more it is something classed, located, measured, compared, assigned to a function, etc., etc.; the more unreservedly do we call the state of mind a perception, and the relatively smaller is the part in it which sensation plays.

_Sensation, then, so long as we take the analytic point of view, differs from Perception only in the extreme simplicity of its object or content._[1] Its function is that of mere _acquaintance_ with a fact. Perception's function, on the other hand, is knowledge _about_[2] a fact; and this knowledge admits of numberless degrees of complication. But in both sensation and perception we perceive the fact as an _immediately present outward reality_, and this makes them differ from 'thought' and 'conception,' whose objects do not appear present in this immediate physical way. _From the physiological_ _point of view both sensations and perceptions differ from 'thoughts'_ (in the narrower sense of the word) _in the fact that nerve-currents coming in from the periphery are involved in their production. In perception these nerve-currents arouse voluminous associative or reproductive processes in the cortex; but when sensation occurs alone, or with a minimum of perception, the accompanying reproductive processes are at a minimum too._

I shall in this chapter discuss some general questions more especially relative to Sensation. In a later chapter perception will take its turn. I shall entirely pass by the classification and natural history of our special 'sensations,' such matters finding their proper place, and being sufficiently well treated, in all the physiological books.[3]

THE COGNITIVE FUNCTION OF SENSATION.

_A pure sensation is an abstraction;_ and when we adults talk of our 'sensations' we mean one of two things: either certain _objects_, namely simple _qualities_ or _attributes_ like _hard, hot, pain;_ or else those of our thoughts in which acquaintance with these objects is least combined with knowledge about the relations of them to other things. As we can only think or talk about the relations of objects with which we have _acquaintance_ already, we are forced to postulate a function in our thought whereby we first become aware of the _bare immediate natures_ by which our several objects are distinguished. This function is sensation. And just as logicians always point out the distinction between substantive terms of discourse and relations found to obtain between them, so psychologists, as a rule, are ready to admit this function, of the vision of the terms or matters meant, as something distinct from the knowledge about them and of their relations _inter se_. Thought with the former function is sensational, with the latter, intellectual. Our earliest thoughts are almost exclusively sensational. They merely give us a set of _thats_, or _its_, of subjects of discourse, with their relations not brought out. The first time we see _light_, in Condillac's phrase we _are_ it rather rather than see it. But all our later optical knowledge is about what this experience gives. And though we were struck blind from that first moment, our scholarship in the subject would lack no essential feature so long as our memory remained. In training-institutions for the blind they teach the pupils as much _about_ light as in ordinary schools. Reflection, refraction, the spectrum, the ether-theory, etc., are all studied. But the best taught born-blind pupil of such an establishment yet lacks a knowledge which the least instructed seeing baby has. They can never show him what light is in its 'first intention'; and the loss of that sensible knowledge no book-learning can replace. All this is so obvious that we usually find sensation 'postulated' as an element of experience, even by those philosophers who are least inclined to make much of its importance, or to pay respect to the knowledge which it brings.[4]

But the trouble is that most, if not all, of those who admit it, admit it as a fractional _part_ of the thought, in the old-fashioned atomistic sense which we have so often criticised.

Take the pain called toothache for example. Again and again we feel it and greet it as the same real item in the universe. We must therefore, it is supposed, have a distinct pocket for it in our mind into which it and nothing else will fit. This pocket, when filled, is the sensation of toothache; and must be either filled or half-filled whenever and under whatever form toothache is present to our thought, and whether much or little of the rest of the mind be filled at the same time. Thereupon of course comes up the paradox and mystery: If the knowledge of toothache be pent up in this separate mental pocket, how can it be known _cum alio_ or brought into one view with anything else? This pocket knows nothing else; no other part of the mind knows toothache. The knowing of toothache _cum alio_ must be a miracle. And the miracle must have an Agent. And the Agent must be a Subject or Ego 'out of time,'--and all the rest of it, as we saw in