Therefore, fácil and nave assonate in á-e; espíritu and líquido, in i-o. If ai occurs in a syllable after an a in the accented syllable, the i rather than the a of the diphthong counts in the assonance.

The obscure sound of which I speak, is sometimes improperly confounded with that of short u; thus a recent writer, who professes great skill in respect to such matters, says, "One of the most common sounds in our language is that of the vowel u, as in the word urn, or as the diphthong ea in the word earth, for which we have no character.

"But if a diphthong precedes, or the accent is on the preceding syllable, the consonant remains single: as, to toil, toiling; to offer, an offering.