Motivated exposition
Motivated exposition is background information delivered at a moment when a character has a genuine reason to say, think or discover it, so the reader absorbs it as a by-product of the scene rather than as an announcement.
The unmotivated version is easy to recognise: "As you know, Bob, the reactor has been unstable since the war." Nobody tells a colleague what that colleague already knows. The line exists for the reader, and the reader can feel it.
The motivated versions all supply a reason for the words to be spoken. Someone present genuinely does not know, and asks. A character uses the fact as a weapon in an argument, so the information arrives as an accusation. The reader finds it in a document, or meets it as a consequence before anyone explains it.
An example from The Runner
The Runner, a feature screenplay by Jeffrey Doka, the editor behind Final Boss Editing, opens with a drug runner, Rich, and his copilot James being chased by an F.B.I. plane over the desert. The audience needs a technical fact to follow what Rich does next, and the script delivers it under a deadline:
RICH
What make is their plane?
JAMES
I can't...
RICH
James!
JAMES
Uh. Beechcraft twin. A baron?
RICH
(to himself, thinking)
Beech Baron. Beech Baron.
Ignoring Rich, James's hands fly over his instruments.
JAMES
God, they're at full bore. Forty seconds before they make us land.
Rich freezes for a moment before he begins twisting dials and resetting coordinates. James gasps.
JAMES
Stop! You'll stall us. We'll drop like a rock! What are you--
RICH
Cabin pressure. Beech Barons have cabin pressure; what happens to pressure when you shake up a coke?
Why it works: the fact about cabin pressure is exposition, but nobody is lecturing. Rich works it out because he has forty seconds to escape, and he says it aloud because James is shouting at him to stop. The audience gets the rule just before they see it matter: over the next two pages the F.B.I. plane follows Rich's dive, its cabin pressure gauge goes red, and its rear windows burst.
A quick test
Delete the exposition and ask whether the scene still has a reason to exist. If its only job was to deliver the fact, it was not motivated. It was a lecture with furniture. For the version that stops a story cold, see info dump.
Timing
Timing matters as much as motive. Information is most welcome just after the reader starts wanting it. Withhold a beat longer than feels comfortable, and the explanation lands as relief rather than homework. When the fact also sets up something that happens later, as the cabin pressure does, it doubles as setup and payoff.
Frequently asked questions
What is motivated exposition?
Motivated exposition is background information that comes out because a character needs it right now: to solve a problem, win an argument or understand a threat. The reader learns it without feeling taught.
What is 'As you know, Bob' dialogue?
It is the classic example of unmotivated exposition: one character telling another something they both already know, purely so the audience hears it. The fix is to give the line to someone who does not know, or to cut it.