They can be a creation of the author who, in addition to the grammatical rules, makes an exception for a creative purpose. The truth is that to carry out poetic licenses, as well as to write poems with free verse, it is very important to be an experienced writer and not a novice since each license has a reason and is not the result of improvisation or ignorance.
This is an art that does not go out of style, as evidenced by the verses of authors such as Pablo Neruda, who continue to move generations later. It can also be said; that the poetic license is considered as those resources that the poet has to adjust his verses to a certain measure and rhyme. These licenses are important for the writer because they allow him to give him characteristics in terms of the form of his creation, giving him the stylistic characteristics of the author and thus giving him the beauty that the poetic text can have.
When talking about these licenses, the characteristics that characterize the poems in terms of measure and rhythm stand out. As for the measure, or call metric of the verses, it can be said that they help to adjust the measure of the verses with respect to the number of syllables of other verses of the same stanza, among them we can mention the synalepha, the hiatus, syneresis and umlauts. For its part, the rhythm has to do with the musicality that the poem's verses must have, that is, its rhyme, which can be consonant and assonance.
For example: let's say the poet wants to make two compositions, a sonnet and a romance.
a) In the first case, to create a sonnet not only the structure of ABBA ABBA CDC DCD must be respected, but also the meter of eleven syllables in each verse, that is, a versification of the main art.
b) In the second case, to make a romance, you must take into account that this structure has an indeterminate number of verses, but always with a cross rhyme: ABCB, and a meter of eight syllables, that is, one less art version.
If the poet, when making the sonnet and the romance, does not obtain the exact meter for each, then he can resort to the use of poetic licenses, which justify the measurement of the syllables in a non-canonical way, but of poetry.
