Why do we say words like "um"?
1) No reason: Father of modern day linguistics, Prof. Noam Chomsky believes such phrases are simply "errors in applying knowledge of language in actual performance."
2) For Control: One school, for example, believes the usage is deliberate - if anticipating a delay in speech, the speaker uses these signals to inform the listener we need a second to formulate our thoughts. Otherwise, the listener may feel the speaker is finished. They say "um" almost always sets up a long delay in speech, while "uh" signals a brief pause. Speakers also extend vowels of words if searching for the next word. They say such "disfluencies" make up 6-10% of spontaneous speech and all languages have these "disfluencies".
3) For Comprehension: Other research argues toddlers use disfluencies to focus on words that follow. As compared with a normal sentence, toddlers over 2 years of age tended to pay more attention when they heard a sentence with "um" or "uh". Researchers argue this is because 2 year olds understand that "uhs" often precede unknowns.
