Full Idea
A motive is equally incapable of action and of passion; because it is not a thing that exists, but a thing that is conceived. …Motives may be compared to advice or exhortation.
Gist of Idea
A motive is merely an idea, like advice, and not a force for action
Source
Thomas Reid (Essays on Active Powers 4: Liberty of Agents [1788], 4)
Book Reference
Reid,Thomas: 'Inquiry and Essays', ed/tr. Beanblossom /K.Lehrer [Hackett 1983], p.335
A Reaction
We say people are motivated by greed or anger or love, which seems a bit stronger than mere advice.