Three might be a crowd but four appears to be the magic number when it comes to conversation. And, according to an academic who has spent decades studying how w

Three might be a crowd but four appears to be the magic number when it comes to conversation. And, according to an academic who has spent decades studying how we socialise, William Shakespeare instinctively understood that. Professor Robin Dunbar, an anthropologist and evolutionary psychologist at the University of Oxford, is known for “Dunbar’s number”, which alludes to his theory that most of us are able to sustain about 150 social connections. But his research has also explored how people act in smaller groups. At Cheltenham Science Festival he explained that when it comes to having an enjoyable chat, the upper limit is a gang of four. When social groups have five or more members, the chances of them laughing together plummets. He said: “You very rarely get more than four people in a conversation. In the normal run of things, when a fifth person joins a group, it’ll become two conversations within about 20 seconds.” Alternatively, a “lecture” situation develops in which one person holds court and the others act as an audience. In larger groups, “you have to decide whether the person who is speaking is really so important you’d rather be standing there saying nothing”, he said. If the speaker is not very interesting, the audience tends to splinter into groups of four or fewer. Dunbar believes that the underlying reason is that we can only track what a certain number of people are likely to be thinking at one time. Scientists call this the “theory of mind”, which involves being able to see the world from another person’s perspective. Also known as “mentalising”, it is crucial for conversation because people often use imprecise language, which makes context important. “The language we use is full of metaphors and unfinished sentences. The listener has to be able to figure out what it is the speaker is trying to say,” said Dunbar. Additionally, the speaker must track whether those they are talking to are following their meaning. Dunbar believes that the limits of our ability to predict the thoughts of others in this way explains why groups that work in challenging situations — such as SAS patrols and surgical teams — tend to do best when there are four members. In The Social Brain, co-authored by Dunbar, he argues that Shakespeare must have intuitively known about this phenomenon as it is rare for his plays to have more than four significant characters speaking in one scene. He wrote: “[Shakespeare] instinctively understood the mentalising capacities of his audience. He was anxious to ensure his audience wasn’t cognitively overloaded by the number of minds in the action on stage. [It is] a masterclass in the study of human psychology.”