Concord is redundancy, and contrary to what could be expected, redundancy results, as a rule, from least effort: people do not mind repeating if mental effort is thereby reduced; if adjectives are quite freely and frequently used as nouns, as was the case of Indo-European languages, it will be indispensable for them to carry the mark of their function if the nouns do; therefore a word like 'fortis', ‘courageous’ or ‘courageous fellow’ is inflected just like 'civis' ‘citizen’ […] But when 'fortis' is really nothing but an attribute of 'civis', it would be more logical either to mark it as such, or to use the bare stem, letting its vicinity to 'civis' indicate its relation to it. But it is certainly much easier to let the the adjectives keep in all cases inflected forms that have had to be memorized anyway.
- Martinet (1962), a pag.55

Depending on various conditions, messages will be more or less repetitious, and this will be determinant for the average handling of language. Redundancy, in various forms, is a basic necessity of linguistic communication. As a matter of fact, human nature is such that a total elimination of redundancy might, in many circumstances, entail a serious increase of the energy spent on the speech […].
- Martinet (1962), a pag.140

It has now become clear that redundancy, grammaticalized or just lexical, is a basic feature of human communication, and it may in particular instances be resorted to in order to indicate the function of some segment.
- Martinet (1962), a pag.56

Redundancy is indispensable for the transmission of the language to new generations of speakers: a good many words are learned through identifying certain aspects of certain situations, say a given animal, the horse, with a certain vocal product […] Learning new words through redundant context is a very common occurrence throughout life, whether this takes place in one’s own or in some foreign language. The importance of redundancy does not, of course, invalidate the concept of a language economy, but reminds us of its complexity […].
- Martinet (1962), a pag.141