In actual present practice, if observers were asked to identify the intensity of John’s toothache on a scale running from zero intensity up, the variability of the reports would be very great in comparison with those of stature or body-temperature. Supposing the most intense toothache to be called _K_, we might well have reports of from say .300 _K_ to .450 _K_, some observers identifying the fact with a condition one and a half times as intense as that chosen by others. But such a variability might also occur in primitive men’s judgments of length or temperature. It is important to note that the accuracy of John’s own identification of it depends in any case on his knowledge of the scale and his power of comparing his toothache therewith. Well-trained outside observers might identify the intensity of John’s toothache more accurately than he could. In the case of John’s anxiety, the most striking fact is the low degree of accuracy in identification. The quality of the anxiety and its intensity would both be so crudely measured by present means that even if the observers were from the score of most competent psychologists, their reports would probably be not much better than, say, the descriptions now found in masterpieces of fiction and drama. Science could not tell at all closely how much John’s anxiety at this particular time resembled either his anxiety on some other occasion or anything else. This inferiority is due in part to the fact that the manifestations of anxiety in behavior, including verbal reports, are so complicated by facts other than the anxiety itself, by, for example, the animal’s health, temperament, concomitant ideas and emotions, knowledge of language, clearness in expression and the like. It is due in part to the very low status of our classification of kinds of anxieties and of our units and scales for measuring the amount of each kind. Hence the variation amongst observers would be even greater than in the case of the toothache, and the confidence of all in their judgments would be less, and far, far less than their confidence in their judgment of John’s stature. The best possible present knowledge of John’s anxiety, though scientific in comparison with ordinary opinion about it, would seem grossly unscientific in comparison with knowledge of his stature or weight. Knowledge of the anxiety would improve with better knowledge of its manifestations, including verbal reports by John, and with better means of classification and measurement.