[...] interjections are merely conventional fixations of the natural sounds. They therefore differ widely in various languages in accordance with the specific phonetic genius of each of these. As such they may be considered an integral portion of speech [...]
- Sapir (1921), a pag.5

[...] the interjections and sound-imitative words of normal speech are related to their natural prototypes as is art, a purely social or cultural thing, to nature.
- Sapir (1921), a pag.6

[...] though the interjections differ somewhat as we pass from language to language, they do nevertheless offer striking family resemblances and may therefore be looked upon as having grown out of a common instinctive base [...]
- Sapir (1921), a pag.6

Interjections are among the least important of speech elements. [...] they, avowedly the nearest of all language sounds to instinctive utterances, are only superficially of an instinctive nature.
- Sapir (1921), a pag.6