the sibilant flatus approaches nearer to the vowels than even the semi-vowels.
As we distinguished between tenuis and media in the consonants, we must admit a twofold intonation for the flatus or the sibilants also. A flatus or sibilant cannot be modified exactly in the same manner as a consonant produced by contact; but, by an analogous process, it may become either "asper" or "lenis," rough or soft. We are best acquainted with this distinction in the primitive and unmodified breathing which necessarily precedes an initial vowel. The spiritus asper and lenis in Greek are modifications of that initial breathing which is inherent in every vowel sound at the beginning of a word or of a syllable. It comes out freely as the spiritus asper in Homer and ὅρος, frontier, while it is tempered and to our ears hardly audible in ʼAristotle and ὄρος, hill. In ancient languages the spiritus asper is frequently represented by the dental flatus (s), and the spiritus lenis by a semi-vowel, as, for instance, the Digamma Æolicum.
The dental flatus, as a tenuis or rather as fatus asper, is heard in sin and seal; while the media or lenis is frequently represented by the English z, as in zeal and breeze.
The sharp labial flatus is the pure f, which the Greeks could not pronounce, and which we hear in "find" and "life." The flat corresponding sound is heard in "vine" and "live." This also is a difficult letter to pronounce, and is therefore avoided by many people, or changed into b, as Scaliger said,
"Haud temere antiquas mutat Vasconia voces,
Cui nihil est aliud vivere quàm bibere."
Strictly speaking, and in accordance with our own definitions, every consonant at the end of a word, unless followed by a slight vocal exhalation such as is heard in drug, loud, sob, must become a tenuis. Now, if we take words where the final consonant is a flatus, but where, by the addition of a derivative syllable, the flatus ceases to be really final, we shall see distinctly how the flatus asper and lenis interchange. The sharp dental flatus is heard in "grass" and "grease." Here the s is really final, although an e is put at the end of grease. If we form the two verbs, to graze and to grease, we have
