(Asked by Tom Lanier of Austin, Texas)

Not everyone says "um", "er" or "ah" when they hesitate while speaking. It depends upon the language.

For example, speakers of Mandarin Chinese often say"zhege" which roughly translates as “this”. In English we say "um", "er", "ah", or other vocalisations for reasons that linguists are not entirely sure about. "Um", "er", and “ah” contain what linguists call "neutral vowel sounds" making them among the easiest sounds to make.

It may be that they can be said without a great deal of thought too. So that may be part of the answer. "Um", "er", and "ah" are what linguists call "fillers". "Fillers" help conversations continue smoothly.

Although we may not consciously realise it, in a two-person conversation, people speak by taking turns. When someone thinks it is their turn to talk, they do. Otherwise, they listen. A two-person conversation becomes like a tennis match. Inevitably there are short periods of silence as people pause to let the other person take over the speaking. But sometimes a speaker doesn’t want to give up their turn and instead wants a little extra time to think about what they’re going to say next. They use a “filler” to signal this.

When a listener hears the “filler”, they continue listening rather than start talking. “Um”, “er”, and “ah” are examples of phonemes. In linguistics, phonemes are the smallest meaningless speech sounds humans make. The smallest meaningful speech sounds humans make are called “morphemes”. Everything we humans say is either meaningless or meaningful. A lot of people never learn the difference. ®

Stephen Juan, Ph.D. is an anthropologist at the University of Sydney. Email your Odd Body questions to s.juan@edfac.usyd.edu.au