Definition of "motive"

there's something in a woman beyond all human delight; a magnetic virtue, a charming quality, an occult and powerful motive.

1624, Democritus Junior [pseudonym; Robert Burton], The Anatomy of Melancholy: […], 2nd edition, Oxford, Oxfordshire: Printed by John Lichfield and James Short, for Henry Cripps, partition III, section 2, member 1, subsection ii

Many of them at first seemed kind to him, but it turned out their motives were not entirely altruistic.

1947, Malcolm Lowry, Under the Volcano, New York: Reynal & Hitchcock

“Your job here is to find the good things in your colleagues—the things their state saw—and not focus on the bad.”I said I understand.“And, Joe, never attack another man’s motive, because you don’t know his motive.”

2007, Joe Biden, Promises to Keep‎, New York: Random House, published 2008, page 110

every joint and motive of her body

c. 1602, William Shakespeare, “The Tragedie of Troylus and Cressida”, in Mr. William Shakespeares Comedies, Histories, & Tragedies […] (First Folio), London: […] Isaac Iaggard, and Ed[ward] Blount, published 1623, [Act IV, scene v]

“Why should Eldridge commit murder? […] There was only one possible motive—namely, he wished to avoid detection as James Selby of Anaconda Ltd. […]”

1931, Francis Beeding, “10/6”, in Death Walks in Eastrepps

In the motive parts of animals may be discovered mutuall proportions; not only in those of Quadrupeds, but in the thigh-bone, legge, foot-bone, and claws of Birds.

1658, Sir Thomas Browne, The Garden of Cyrus, Folio Society, published 2007, page 195