The theory was known as Speech Accommodation Theory until it included non-verbal aspects of communication then it became popular as ' Communication Accommodation' Theory. The theory talks about, people wanting to portray their positive identity to others.
They tend to match their own vocabulary, accent and cadence as of other interactants.
Communication accommodation theory (CAT) is a theory of communication developed by Howard Giles.
It argues that, "When people interact they adjust their speech, their vocal patterns and their gestures, to accommodate to others." It explores the various reasons why individuals emphasize or minimize the social differences between themselves and their interlocutors through verbal and nonverbal communication.
Whether you realize it or not, and it can be either conscious or unconscious, you match your accent, your speed, your rhythm, your vocabulary and even your stance and gestures to that of the person you are talking to.
The main reason a person does this is to show agreement and affinity for another.
If you have ever found yourself matching the vocabulary, speed and cadence of the person you are talking to, you have experienced firsthand an illustration of Communication Accommodation Theory. On the other hand, if you delighted in using the same slang words your peers used when you were a teenager, in spite of the way it frustrated your parents and teachers, you also have firsthand experience with another aspect of Communication Accommodation Theory called divergence.