[2528.] Ascending and Descending Rhythms. Rhythms in which the thesis follows the arsis (as in iambics) are called ascending; those in which it precedes the arsis (as in trochaics) are termed descending.
[2529.] The ancients recognized both ascending and descending rhythms ([2528]), and regarded the former class as at least equal in importance to the latter; but many modern scholars since the time of Bentley have preferred to treat all rhythms as descending, regarding the first arsis of an ascending rhythm as merely answering to a preliminary upward beat in music. Such an initial arsis was named by Gottfried Hermann Anacrūsis (Gr. ἀνάκρουσις, a striking up).
Scholars have been influenced to adopt the anacrustic theory in its widest extent largely by the fact that in most modern music a measure must commence with a downward beat, a rule which did not hold in ancient music. By this theory an iambic verse becomes trochaic with anacrusis, an anapaestic verse dactylic with anacrusis, &c. But in many cases those kinds of verse which begin with an arsis were subject to different rules of construction from those which begin with a thesis. Hence it seems best to restrict anacrusis to logaoedic verse, in which it undoubtedly occurs.
[2530.] The anacrusis may be a long syllable, a short syllable, or two shorts (but not two longs). It is often irrational ([2524]). In metrical schemes it is often set off from the rest of the verse by a vertical row of dots: thus, ⁝
[2531.] A group of two feet is called a dipody, one of three a tripody, one of four a tetrapody, one of five a pentapody, and one of six a hexapody. The dipody is the measure of trochaic, iambic, and anapaestic verse. Other kinds of verse are measured by the single foot.
A single foot is sometimes called a monopody. A group of three half feet, i.e. a foot and a half, is sometimes called a trithemimeris, one of two and a half feet a penthemimeris, one of three and a half a hephthemimeris, &c.
[2532.] A Rhythmical Series, Rhythmical Sentence, or Colon is a group of two or more feet (but not more than six) which are united into a rhythmic whole by strengthening one of the ictuses, so that it becomes the principal or dominant ictus of the whole group.
[2533.] The Verse. A rhythmical series, or group of two (or even three) series, which forms a distinct and separate whole is called a Verse. The final syllable of a verse must terminate a word (except in cases of synapheia, see [2510]), and may be either long or short (whence it is termed syllaba anceps) without regard to the rhythm. Hiatus ([2474]) is freely allowed at the end of a verse (though in rare cases elision occurs before a vowel at the beginning of the following verse; see [2492] and [2568]).