Having thus dealt with the problem of how the neuro-muscular mechanisms of the body generate and maintain the meanings of words, let us now return to the original question of this chapter, namely, What is the ultimate reason why we employ such pairs of antonyms as “good” and “bad” in our judgments of praise or blame, our expressions of desire or aversion, and in our estimations of merit or defect? Our answer is that the felt opposition and contradiction of antonyms is due to the conflict of motor tendencies, and in support of this theory we cite a well-recognized physiological principle,—the law of reciprocal innervation. _The Physiological Explanation of the Opposition of Antonyms_ Every freely moving part of the body, such as the leg, the arm, and the head, is equipped principally with two sets of muscles, called, from their functions, the _flexors_ and the _extensors_. The flexors are those muscles which for example, upon contracting, draw the legs and the arms toward the body and fold them close to it, and which lower the head upon the chest; while the extensors stretch out the arms and legs, open wide the hands, and raise the head to an erect posture. Other parts of the body are similarly equipped for producing motions of an opposite character in the skeletal system.[4] The eyeballs are lowered by the use of a different muscle than that by which they are elevated; the muscle which depresses the wings of the nose is a direct antagonist of the other muscles which control the movements of this organ, and so on throughout the whole of our movable bodily structures. Moreover, when one such pair of muscles is contracted, the opposed member is normally relaxed, and vice versa; or, as the physiologist would say, the two muscles are reciprocally innervated.[5]