These words all denote stimuli that prompt one to action. Motive connotes some impulse within a person – such as love, hate, revenge or ambition – that impels him to act with a strong sense of purpose: The police knew that the murderer’s motive was jealousy; His real motive for joining the club was not to make new friends, but to try to meet potential clients.

Reason is the most general of these words, but in a specific sense it implies a logical justification, either to oneself or to others, for an actions, by citing facts and circumstances.

• His reason for entering the hospital was to undergo surgery; A severe handicap was the reason for his shyness.

Reason may sometimes hint at a contrived excuse: Although he had overslept, the reason he gave for his lateness was that he had been caught in a traffic jam.

Incentive and spur are reasons for undertaking action with extra zeal. Incentive nearly always implies a reward for such effort: prizes offered as an incentive to salesmen. Spur suggests more strongly than does incentive something external to oneself that causes a sudden increase in the rate of activity, as suggested by the original meaning of the word in horsemanship: Finding the cause of a disease will provide a spur for research on a cure for it.

Inducement denotes an attractive reason for choosing one thing rather than another. The promise of a yearly bonus may be an inducement to an executive who is considering a job offer.