These words refer to whatever causes or contributes to the starting or continuing of an action. Impel always suggests considerable force; sometimes this can apply to the movement of physical objects: an upward rush of sparks, impelled by columns of smoke that erupted from the burning buildings. More often, the word refers to people acting under strong outward constraint or inner necessity: refugees impelled to flee before the advancing armies; legislators impelled by popular opinion to campaign for the passage of a bill; impelled by his desire to see her once more. Move is much more general; it can refer to physical motion without reference to force: the earth moves round the sun. when applied to the behaviour of people, it stresses one aspect of impel , namely, a forceful inner conviction or depth of feeling: moved by her appeal to enter the fight in her behalf. Just as often, the word refers to any surge of emotion: moved to tears; a film that he had found very moving .

Like impel , driven can suggest considerable force in reference to physical objects: leaves driven by the wind. It contrasts with impel because of its greater informality. In reference to what causes people to act, it can suggest a more direct outward goading than impel , or a greater inner obsessiveness than move: Christ driving the money changes from the temple; driving off the flies with a fly-swatter; a psychosis that drove him to act out his fantasies in reality; driven to drink by a nagging wife. Motivate is mostly restricted to expressing what causes people to act. It can be used in neutral causal explanation; What motivated him to commit the murder? Or it can indicate a conscious attempt to inculcate a desire for something: students motivated to learn by the encouragement of a good teacher.

Where all the previous words are as equally applicable to initial as to continuing action, prod and prompt both emphasize setting something into motion. At its most literal, prod suggests the use of some sort of tool: He prodded the anthill with a stick. When applied to human behaviour, the word suggests an isolated impetus of any sort: a smell of smoke that prodded the sleeping parents into action; a book that prodded the nation into a belated concern for the impoverished. Prompt literally refers to giving a speaker a cue to his lines, as in the theatre. He still had to be prompted after two weeks of rehearsing; a television prompting device for speakers delivering written speeches. In more general uses, the word is like prod in suggesting any sort of stimulus to action. But where prod often suggests a start or jolt that makes one newly aware of something, prompt is more like motivate, though less formal, in its emphasis on causation: a misstatement of fact that prompted him to disagree with his host for the first time that evening; What prompted him to behave so rudely to his guests?