-s_ in the second tends to obscure the inherent value of
the accentual alternation. This value comes out very neatly in such
English doublets as _to refund_ and _a refund_, _to extract_ and _an
extract, to come down_ and _a come down_, _to lack luster_ and
_lack-luster eyes_, in which the difference between the verb and the
noun is entirely a matter of changing stress. In the Athabaskan
languages there are not infrequently significant alternations of accent,
as in Navaho _ta-di-gis_ "you wash yourself" (accented on the second
syllable), _ta-di-gis_ "he washes himself" (accented on the first).[52]

[Footnote 52: It is not unlikely, however, that these Athabaskan
alternations are primarily tonal in character.]

Pitch accent may be as functional as stress and is perhaps more often
so. The mere fact, however, that pitch variations are phonetically
essential to the language, as in Chinese (e.g., _feng_ "wind" with a
level tone, _feng_ "to serve" with a falling tone) or as in classical
Greek (e.g., _lab-on_ "having taken" with a simple or high tone on the
suffixed participial _-on_, _gunaik-on_ "of women" with a compound or
falling tone on the case suffix _-on_) does not necessarily constitute a
functional, or perhaps we had better say grammatical, use of pitch. In
such cases the pitch is merely inherent in the radical element or affix,
as any vowel or consonant might be. It is different with such Chinese
alternations as _chung_ (level) "middle" and _chung_ (falling) "to hit
the middle"; _mai_ (rising) "to buy" and _mai_ (falling) "to sell";
_pei_ (falling) "back" and _pei_ (level) "to carry on the back."
Examples of this type are not exactly common in Chinese and the language
cannot be said to possess at present a definite feeling for tonal
differences as symbolic of the distinction between noun and verb.

There are languages, however, in which such differences are of the most
fundamental grammatical importance. They are particularly common in the
Soudan. In Ewe, for instance, there are formed from _subo_ "to serve"
two reduplicated forms, an infinitive _subosubo_ "to serve," with a low
tone on the first two syllables and a high one on the last two, and an
adjectival _subosubo_ "serving," in which all the syllables have a high
tone. Even more striking are cases furnished by Shilluk, one of the
languages of the headwaters of the Nile. The plural of the noun often
differs in tone from the singular, e.g., _yit_ (high) "ear" bu