A discourse marker is a word or a phrase that plays a role in managing the flow and structure of discourse. Since their main function is at the level of discourse (sequences of utterances) rather than at the level of utterances or sentences, discourse markers are relatively syntax-independent and usually do not change the truth conditional meaning of the sentence. Examples of discourse markers include the particles oh, well, now, then, you know, and I mean, and the discourse connectives so, because, and, but, and or. The term discourse marker was coined by Deborah Schiffrin in her 1988 book Discourse Markers.
In Practical English Usage, Michael Swan defines a discourse marker as "a word or expression which shows the connection between what is being said and the wider context". For him, a discourse marker is something that either connects a sentence to what comes before or after, or indicates a speaker's attitude to what he is saying. He gives three examples: on the other hand; frankly; as a matter of fact. Ian McCormick's The Art of Connection outlines nine classes of connectives based on their purpose:
McCormick points out that "FANBOYS" is mnemonic to recall co-ordinating conjunctions: for, and, nor, but, or, yet, so.
Common discourse markers used in the English language include "you know", "actually", "basically", "like", "I mean", "okay" and "so". Data shows that discourse markers often come from different word classes, such as adverbs ("well") or prepositional phrases ("in fact"). The process that leads from a free construction to a discourse marker can be traced back through grammaticalisation studies and resources.
Traditionally, some of the words or phrases that were considered discourse markers were treated as "fillers" or "expletives": words or phrases that had no function at all. Now they are assigned functions in different levels of analysis: topic changes, reformulations, discourse planning, stressing, hedging, or backchanneling.
Another example of an interpersonal discourse marker is the Yiddish marker nu, also used in Modern Hebrew and other languages, often to convey impatience or to urge the listener to act (cf. German cognate nun, meaning "now" in the sense of "at the moment being discussed," but contrast Latin etymological cognate nunc, meaning "now" in the sense of "at the moment in which discussion is occurring"; Latin used iam for "at the moment being discussed," and German uses jetzt for "at the moment in which discussion is occurring").