Number is evidently felt by those who speak English as involving a necessary relation, otherwise there would be no reason to express the concept twice, in the noun and in the verb.
- Sapir (1921), a pag.87

There are [...] languages in which the plural [...] is conceived of in the same [...] spirit in which we feel the negative in unhealthy. For such languages the number concept has no syntactic significance whatever, is not essentially conceived of as defining a relation, but falls into the group of derivational or even of basic concepts.
- Sapir (1921), a pag.94

[...] in all the languages that we have most familiarity with- the idea of number is not merely appended to a given concept of a thing.[...] It infects much else in the sentence, molding other concepts, even such as have no [...] relation to number [...]
- Sapir (1921), a pag.95