These words refer to things that change frequently or rapidly, or to unstable or disloyal natures. Inconstant and fickle are formal and informal terms, respectively, for unfaithfulness, usually in love. Inconstant , however, can apply to a single betrayal of love, whereas fickle applies to the habit of moving from one light or trivial infatuation to another: a fiancé who proved to be inconstant : career-girl hoydens who are fickle and promiscuous. Inconstant can sometimes refer more widely to anything showing variability: desert oases whose wells give an inconstant supply of fresh water; a politician who had been inconstant in his devotion to the principles of his party. In wider uses, fickle still applies to the basic situation of loyalty: young idealists who often prove to be fickle in their choice of causes to uphold.

Changeable and erratic are much more general than the previous pair and are less disapproving in tone. Changeable can register the neutral fact that something is capable of change: the changeable patterns of watered silk. Indeed, this capacity can be desirable: a camera with changeable shutter speeds. More often, however, the word carries a negative tone in reference to people who habitually and readily take up and discard attitudes or opinions: a changeable sort of person who favoured the war one day and opposed it the next. Erratic points more to an uneven or arbitrary course: the erratic path of the rivulet; an erratic fellow whose actions were usually completely unpredictable.

Chameleonic is most comparable to changeable and capricious to erratic , but both words are alike in being more vivid than the foregoing and in being more exclusively concentrated on human characteristics. Chameleonic refers to the chameleon’s ability, as a defensive camouflage, of changing colour so as to blend with its background. Sometimes the word applies to human versatility in a neutral or approving way: students who are chameleonic in the diversity of their extracurricular activities; chameleonic in the way he could make himself at home among all sorts of people. More often the word suggests an insincere person willing to play and role that might be of momentary advantage to him: a chameleonic candidate who took pro-labour stands before union audiences and pro-business stands at chamber-of-commerce dinners. Capricious , which is exclusively negative in tone, need not suggest insincerity, like chameleonic , but it does stress an arbitrary and high-handed attitude in which unfair choices are made, not on the merits of a case, but on the basis of personal taste or whim: a drama critic who seemed capricious in the way be bestowed praise or blame; a woman who was haughty and capricious towards her servants.

Mercurial and protean , alone of these words, may suggest rapidity as well as frequency of change. Mercurial is most comparable to chameleonic , but where a negative tone preponderates in the latter’s use, mercurial is more dependent on context to establish approval or disapproval. In favourable reference, it suggests a highly charged and energetic mental dexterity that is flexible to the demands of specific situations and responsive to opportunities for exploiting such situations to best advantage: a mercurial artist who completely transformed the artistic possibilities of ever medium he worked in. in negative uses, the word suggests an excessively volatile quickness and impatience that results in poor control and botched efforts: too mercurial to sit down and do the painstaking work of revision that his brilliant first drafts sorely needed. Protean refers to the ability of the demi-god Proteus to change shapes as a way of eluding capture; often, protean can function identically with chameleonic in both positive and negative ways. Most often, however, the word refers favourably to someone gifted with diverse abilities and skills which are exhibited in a remarkable proliferation of accomplishments: Michelangelo’s protean imagination. Sometimes, the word refers more neutrally to anything given to change: a period of crisis in which the same basic dilemma appeared again and again in protean forms.