II.
9. Pleasure and Pain have been treated in relation by masters of thought from the earliest times. By one we find them called opposites; another speaks of them as related as heat is to cold. Now, pain is looked upon as normal and pleasure as its mere absence; again, pleasure is held to be normal and pain its mere negation: but the bond of relation between the two is rarely questioned and is usually conceded. It appears to me that this weight of authority cannot properly be ignored: such a full expression of the observation of mental states by thoughtful men is clearly a datum of Psychology which cannot be passed over by scientific psychologists in their consideration of this subject. Sufficient ground for these statements of relation appears in the fact that Pleasure and Pain arise in consciousness as disparate parts of a continuum. One fades into the other, when there is no other observed change in the nature of the mental elements presented at the same time. Strong stimuli, if continuous, gradually fail in the production of pleasure and as gradually become pain producers. One displaces the other. Apparently no element of consciousness can be both pleasurable and painful at the same time: the one appears to exclude the other, although it seems equally certain that psychoses composed of diverse elements may have in their make-up coexistent elements both pleasurable and painful. It is the judgment of common sense that Pleasure and Pain are two states, too disparate to be commonly known by any one word, but so inseparably connected that they must be mentioned in one breath. I have dwelt upon this matter a little at length, because there seems to be nowadays a tendency to ignore this relation.
Since the sensations of heat and cold, which are held in relation, have been found to have specific nerves and corresponding terminals, the fact of the relation between Pleasure and Pain would be no objection to the Sensational view were it not for the fact that while the discovery of pain nerves has been claimed, there is not the slightest indication of the existence of pleasure
