Some [...] grammatical processes, like suffixing, are exceedingly wide-spread; others, like vocalic change, are less common but far from rare; still others, like accent and consonantal change, are somewhat exceptional as functional processes.
- Sapir (1921), Pag. 59

Consonantal change as a functional process is probably far less common than vocalic modifications, but it is not exactly rare.
- Sapir (1921), Pag. 74

The chief difficulty in isolating accent as a functional process is that it is so often combined with alternations in vocalic quantity or quality or complicated by the presence of affixed elements that its grammatical value appears as a secondary rather than as a primary feature.
- Sapir (1921), Pag. 79