Some rules must be present; otherwise conversations would be continually breaking down into a disorganized jumble of interruptions and simultaneous talk. In many formal situations, such as committee meetings and debates, there are often explicit markers showing that a speaker is about to yield the floor, and indicating who should speak next (e.g. ‘I think Mr. Smith will know the answer to that question').
This can happen in informal situations too (‘what do you think, John'?), but there the turn-taking cues are usually more subtle.
People do not simply stop talking when they are ready to yield the floor. They usually signal some way in advance that they are about to conclude.
The clues may be semantic (‘So, anyway, ....','Last but not least .....'); but more commonly the speech itself can be modified to show that a turn is about to end – typically, by lowering its pitch, loudness, or speech Body movements and patterns of eye contact are especially important. While speaking, we look at and away from our listener in about equal proportions; but as we approach the end of a turn, we look at the listener more steadily. Similarly, when talking to a group of people, we often look more steadily at a particular person, to indicate that in our view this should be the next speaker.
Listeners are not passive in all of this. Here too there are several ways of signalling that someone wants to talk next. Most obviously, the first person in a group actually to starts speaking, after the completion of a turn, will usually be allowed to hold the floor.
More subtly, we can signal that we want to speak next by an observable increase in body-tension by leaning forward, or producing an audible intake of breath. Less subtly, we can simply interrupt a strategy which may be tolerated, if the purpose is to clarify what the speaker is saying, but which more usually leads to social sanctions.