Watson has recently stated that a similar substitution of one stimulus for another occurs in the case of an emotional reaction as well as at the level of the simple physiological reflex response.[8] This means that when an emotionally exciting object stimulates the subject simultaneously with one not emotionally exciting, the latter may in time (or even after one joint stimulation) arouse the same emotional response as the former. Kempf considers this capacity of the emotion to become thus conditioned to other than the original stimuli "of the utmost importance in determining the selections and aversions throughout life, such as mating, habitat, friends, enemies, vocations, professions, religious and political preferences, etc."[5] Just as Pavlov and his followers found that almost anything could become a food sign, so the study of neurotics has shown that the sexual emotion can be fixed upon almost any love object. For example, a single characteristic of a beloved person (e.g.,--eye colour, smile posture, gestures) can become itself a stimulus to evoke the emotional response originally associated only with that person. Then it happens that the affection may centre upon anyone possessing similar traits. In most psychological literature, this focussing of the emotion upon some particular characteristic is termed _fetishism_, and the stimulus which become capable of arousing the conditioned emotional response is called an _erotic fetish_. In extreme cases of fetishism, the sexual emotions can only be aroused in the presence of the particular fetish involved. Krafft-Ebing[6] and other psychopathologists describe very abnormal cases of erotic fetishism in which some inanimate object becomes entirely dissociated from the person with whom it was originally connected, so that it serves exclusively as a love object in itself, and prevents a normal emotional reaction to members of the opposite sex. The development of romantic love has depended to a great extent upon the establishment of a wide range of stimuli capable of arousing the erotic impulses. As Finck has pointed out, this romantic sentiment is inseparable from the ideals of personal beauty.[3] As criteria of beauty he lists such characteristics as well-shaped waist, rounded bosom, full and red underlip, small feet, etc., all of which have come to be considered standards of loveliness because the erotic emotion has been conditioned to respond to their stimulation. Literature is full of references to such marks of beauty in its characters (_Jane Eyre_ is almost the only well-known book with a plain heroine), and is therefore one of the potent factors in establishing a conditioned emotional reaction to these stimuli.