the.com/motive

The invisible engine that every detective chases and every villain swears they didn't have.

means The reason or inner drive that prompts someone to act in a particular way.

from From Latin 'motivus,' meaning 'moving' or 'serving to move,' built on 'movere,' to move (the same root that powers 'motion,' 'motor,' and 'emotion'). It came into English through Old French in the late medieval period, carrying the literal sense of something that sets things in motion — only later did it slip inward to mean the thing that sets a person in motion.

art term
In music, a motif is a recurring fragment driving a piece
latin root
From movere, to move — same family as motor
legal weight
Proving it strengthens a case but isn't required for conviction
design world
A repeated decorative pattern is also called a motive
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