Do you want serious conversation? Stick to four. Just ask Shakespeare.
Researchers who have time on their hands have figured out that four is the right number for chatting. If you invite more, the quality of discourse will decline and the stress level of the participants till increase.
This is all related to the ability to understand that other people do not necessarily know or intend the same things that we ourselves do, Frank McAndrew, a psychology professor, writes. If two people are engaged in conversation, each must understand what his or her partner intends and what each person understands about the other’s state of mind. So the more people you add the harder this juggling gets.
Other researchers with nothing better to do have determined that this is evolutionary.
If there are three people in the conversation, there are three possible pairs, only one of which excludes you. If there are five people, there are 10 possible pairs, and the majority—six—don’t include you, which makes it harder to get your point across.
What if, the researchers argue, there was an evolutionary advantage to not being “outnumbered” in a conversational group? The physical danger of being an isolated outcast is clear: exclusion from society in early human history could easily be a death sentence, and even most observed cases of lethal chimpanzee violence have happened when aggressive groups encounter a lone chimp.
Here's the Shakespeare angle.They analyzed the conversations in 10 different plays by William Shakespeare. Scholars have long been aware that conversational patterns in Shakespearean plays accurately reflect the dynamics of real-life social interactions — which is one reason their appeal has endured over time. If this is the case, it would be interesting to find out if Shakespeare applied the “maximum size of a conversation” rule to the characters in his plays. Krems and her colleagues discovered that no conversation in any play they analyzed ever involved more than five characters,
Finally, when inviting people over, remember The Bard's rule: "“Better a witty fool, than a foolish wit.”~ Excursus