[...] speech is so inevitably bound up with sounds and their articulation that we can hardly avoid giving the subject of phonetics some general consideration. [...] neither the purely formal aspects of a language nor the course of its history can be fully understood without reference to the sounds in which this form and this history are embodied.
- Sapir (1921), Pag. 42

Languages can change at so many points of phonetics, morphology, and vocabulary [...]
- Sapir (1921), Pag. 152

'Phonetic laws' make up a large and fundamental share of the subject-matter of linguistics. Their influence reaches far beyond the proper sphere of phonetics and invades that of morphology, as we shall see.
- Sapir (1921), Pag. 173

[...] we do not yet understand the primary cause [...] of the slow drift in phonetics, though we can frequently point to contributing factors.
- Sapir (1921), Pag. 183

Every linguist knows that phonetic change is frequently followed by morphological rearrangements, but he is apt to assume that morphology exercises little or no influence [...] I am inclined to believe that our [...] tendency to isolate phonetics and grammar as mutually irrelevant linguistic provinces is unfortunate.
- Sapir (1921), Pag. 183

In phonetics, as in vocabulary, we must be careful not to exaggerate the importance of interlinguistic influences.
- Sapir (1921), Pag. 201