It has its own diction and imagery, conforming to the order, gradations and subtleties of its thought. Like other forms of genius, too, it is permitted certain liberties and variations of language or expressions in order to avoid monotony and maintain the life and music of the verse. These are more strictly rhetorical, however, and next in importance to the poetic content is poetic form.
By poetic form we mean the mould and measure whereby, in English, poetry gets itself into the expression adapted to produce its designed effect.
Metre.—All impassioned language, as in eloquence for instance, tends to fall into a more or less regular rhythmic swing. In poetry, which is both impassioned and imaginative, this rhythm is timed to definite lengths and called metre, which is the Greek word for measure.
The unit of poetic measure is the foot. A foot is a combination of syllables, two or three distinguished, after the Greek, as long and short, but more truly accented and unaccented, because our syllabic values, unlike the Greek, are more accentual than quantitative. A variety of poetic feet are employed in English, whose names and values are derived from Greek prosody.
Poetic Feet.—For brevity of description a notation is used to designate the foot: the sign (—) for a long, and (◡) for a short syllable. The kinds of feet in most common English use, here marked by their signs and illustrated by a word, are: Iambic or Iambus, a short and a long (◡ —, e. g. forbid); Trochaic or Trochee, a long and a short (— ◡, e. g. lightly); Spondaic or Spondee, two longs (— —, e. g. all day); Anapestic, two shorts and a long (◡ ◡ —, e. g. arabesque); and Dactylic, a long and two shorts (— ◡ ◡, e. g. silently).
Other feet, such as Tribrach, three shorts (◡ ◡ ◡, e. g. rapidly); Amphibrach, short long short (◡ — ◡, e. g. tremendous), and Amphimacer, long short long (— ◡ —, e. g. undismayed), are used less frequently, and only as blends with other measures.
Verse.—The first combination of poetic feet results in the verse or line, somewhat analogous to the clause in a prose sentence. The word verse means by derivation a turning; perhaps because where it reaches a certain designed length the writer turns back and begins a new line. The kinds of verse employed are named by Greek names according to the number of feet they contain; and along with this, if the measure is fully described, is named the kind of foot.
The same notation as given above is kept up through the line, the feet being separated by an upright line. Thus, taking the Iambic foot as unit, we note: Monometer, one-measure, or one foot long (◡ —); Dimeter, two-measure (◡ — | ◡ —); Trimeter, three-measure (◡ — | ◡ — | ◡ —); Tetrameter, four-measure (◡ — | ◡ — | ◡ — | ◡ —); Pentameter, five-measure (◡ — | ◡ — | ◡ — | ◡ — | ◡ —); and Hexameter, six-measure, (◡ — | ◡ — | ◡ — | ◡ — | ◡ — | ◡ —). English names are sometimes used, as 8 and 7, or fourteeners.
A few poetic lines may here be given, with their notation, by way of illustration: