An important but often understudied area in linguistics is the study of speech errors. A speech error can be defined as a conscious or unconscious deviation from a speech utterance. Five kinds of speech errors are omission, addition, metathesis, substitution and word exchange.
An example of omission is the utterance "They can come" instead of "They can't come." Here the word-final "t" of "can't" is omitted.
Addition is the exact opposite. In this case, more is uttered than is intended. For example, the phrase "us and me" in "He saw us and me" instead of "He saw us" is an example of addition.
Metathesis is a speech error in which segments switch place in an utterance. The utterance "feel run" instead of the intended "real fun" is an example of metathesis. Here the word-initial "r" of "real" and word-initial "f" of "fun" switch position.
In substition, one word is substituted for another. For example, the utterance "I can't find my bat" instead of the intended "I can't find my ball" is substituton. This kind of utterance often occurs with words which sound similar to one another.
Word-exchange is similar to metathesis. However, it is not segments which are exchanged but rather words. For example, "I must put the pot in the rice" instead of the intended utterance "I must put the rice in the pot" is an example of this type of error.
Speech errors can be categorized into many different kinds. They are deviations from intended utterances which speakers may or may not be conscious of. If they are not conscious of their error, they cannot correct it. Among the most common speech errors are omission, addition, metathesis, substitution and word exchange.