Anacoluthon is a figure of speech in which the grammatical flow of a sentence is disrupted, often to begin another sentence. It can be done either intentionally, as a rhetorical device, or unintentionally, in which case it would constitute a grammatical error. Common uses of anacoluthon include to imitate speech or thought and to move an important piece of information to the beginning of a sentence.
In casual conversation, people often speak in ways that would not be considered grammatical in formal speech or writing. Anacoluthon is one example of this and might be used in writing to imitate informal, confused or ungrammatical speech. For example, if a fiction author were describing the speech of a character who is waking up after a traumatic head injury, he or she might write, "The last thing I saw was the — Where did the elephant go, anyway?" This would be ungrammatical speech on the part of the character, but potentially excellent rhetoric on the part of the writer.
This type of anacoluthon is common in poetry, especially plays or dramatic monologues. The Victorian poet Robert Browning, for instance, often wrote dramatic monologues from the perspective of characters who were frequently a little off-beat — if not outright crazy. In his poem "Mr. Sludge, the Medium," a fake spiritist pleads with an angry customer not to expose his trickery: "You gave me — (very kind it was of you) / These shirt-studs." The interjection of the non-grammatical "very kind it was of you" emphasizes the speaker's frenzied nervousness.
Another use of anacoluthon is in stream-of-consciousness, which is intended to represent thoughts as closely as possible. Since thoughts are not always completely coherent and rarely fully grammatical, this style of writing lends itself to anacoluthon. Stream-of-consciousness writing was popularized in the Modernist literary era by writers like James Joyce.
As a rhetorical device in non-fiction writing or speech, anacoluthon can sometimes be used to place the topic to the beginning of the sentence, even though it might not fit there grammatically. For instance, someone might say, "Those puppies peering over the edge of the building — do you think they're in danger of falling?" Placing "those puppies" at the beginning of the sentence alerts the hearer to the topic of conversation immediately, which might be advantageous if the puppies are actually in danger.
Anacoluthon is classified as a "figure of disorder" in rhetoric. In general, a figure of disorder is any sentence with syntax that does not match up with what is expected. It should not, however, be confused with hyperbaton, another figure of disorder that refers to moving a word or phrase out of its expected position in the sentence.