Anacoluthon

Anacoluthon (Greek: 'not following') is the figure in which a sentence begins with one grammatical structure and, before finishing, switches to another. In casual speech it is an error; in careful writing it is a deliberate figure used to represent thought as it actually happens — a mind changing its mind in real time.

The distinctive effect is that the sentence feels honest. A polished sentence has been through a mental editor before it reached the page; an anacoluthon has not. This is why the figure appears constantly in the interior monologues of modernist fiction (Woolf, Joyce, Faulkner), in the transcribed speech of politicians under pressure, and in first-person essays that want to feel intimate.

Compared to aposiopesis, which stops entirely, and anaphora, which repeats a beginning, anacoluthon is the figure of the mid-sentence swerve. 'If only he had — but you know how these things end.' The dash signals the swerve; the second half of the sentence has no grammatical relation to the first.

Careful writers use anacoluthon in dialogue to distinguish characters. A character who speaks in complete, closed sentences reads as controlled or cold; a character whose sentences swerve reads as thinking on the run. It is one of the fastest ways to give a piece of dialogue a pulse.

In formal writing (legal, technical, academic) anacoluthon is almost always an error, because the reader is looking for precise reference. In creative writing it is a legitimate figure — but, as with all figures of interruption, best used sparingly.