A motive is a desire, need, or emotion that prompts or causes a person to act in a certain way; it is an inner urge that produces an act, but it also applies to the result of action: "Jeb's motive was to get even with those who had not helped him." "Fear was his motive in trying to escape." An incentive is something offered as a reward or prize, especially one proffered to spur competition: "Profit sharing is an incentive for every employee in this company." Motif comes from the same French word as motive, but it means (1) "a dominant idea or feature," (2) "a recurring subject or theme in an artistic work," and (3) "a distinctive form or shape in a design": "Isn't the profit motif the principal guide in every business?" "The motif of Verdi's Rigoletto differs from that of his "Il trovatore." "I like the motif of this wallpaper." Words allied in meaning to motive and incentive are stimulus, spur, inducement, incitement, impulse, goad, prod, and encouragement.
Dictionary of problem words and expressions. Harry Shaw. 1975.