The two essentials of Spanish poetry are (1) a fixed number of syllables in each verse (by verse we mean a single line of poetry); (2) a rhythmical arrangement of the syllables within the verse. Rime and assonance are hardly less important, but are not strictly speaking essential.
SYLLABLE-COUNTING
FINAL SYLLABLES
When a verse is stressed on the final syllable, it is called a verso agudo or masculine verse.
When a verse is stressed on the next to the last syllable, it is called a verso llano or feminine verse.
When a verse is stressed on the second from the last syllable, the antepenult, it is called a verso esdrújulo.
For the sake of convenience, the verso llano is considered the normal verse. Thus, in an eight-syllable verse of this type the final stress always falls on the seventh syllable, in a six- syllable verse on the fifth syllable, etc., always one short of the last. In the case of the verso agudo, where the final stress falls on the final syllable, a verse having actually seven syllables would nevertheless be counted as having eight. One syllable is always added in counting the syllables of a verso agudo, and, contrariwise, one is always subtracted from the total number of actual syllables in a verso esdrújulo. These three kinds of verses are frequently used together in the same strophe (copla or stanza) and held to be of equal length. Thus:
Turbios sus ojos,
Sus graves párpados
Flojos caer.