Because of agreement – a requirement in many languages that the form of different words in a phrase or clause correspond with one another – the same semantic information may be expressed several times.
For example, the English phonemes /p/ and /b/ in the words pin and bin feature different voicing, aspiration, and muscular tension.
According to psychologist Steven Pinker, "In the comprehension of speech, the redundancy conferred by phonological rules can compensate for some of the ambiguity of the sound wave.
Redundancy happens when the repetition of a word or idea does not add anything to the previous usage; it just restates what has already been said, takes up space, and gets in the way without adding meaning.
[5] Computer scientist Donald E. Knuth, author of highly acclaimed textbooks, recommends "to state things twice, in complementary ways, especially when giving a definition.