Francesco Petrarch (1304-1374), an early Renaissance poet, wrote more than 300 sonnets addressed to Laura, a lady forever unobtainable. Thus, he established the model of love poetry that prevailed for the next two centuries, imitated by many writers, Shakespeare included. Along with its prescribed form, the Petrarchan sonnet had the following conventions:
The lady to whom the poem is addressed is forever beyond reach - she is on a pedestal; the poet's love for her is unrequited; the poet is sick to death with love; the lady is described with encomiums almost insincere; and the poet's love is expressed in religious terms.
However, Shakespeare was not a slave to the traditions of the Petrachan form. He breaks with that tradition by burying one Petrachan sonnet and the first four lines of a second within the dramatic action of Romeo's first spoken encounter with Juliet in Act 1, Scene 5, lines 93 to 110.
Romeo begins his Juliet wooing with four lines of conventional Petrarchan language; and there is religious terminology throughout their exchange. But in the second quatrain (lines 97-100), spoken by the poet's lady, it is very clear that Juliet is not aloof - no pedestal for her. In their verbal foreplay before the first kiss, Juliet matches her wooer word for word, line for line. She and Romeo are very well aware of the conventions and operate within them with dexterity, but perhaps galvanized by the headiness of forbidden love, they strive to break them - just as Shakespeare both conformed to and transcended the Petrachan form. As they complete their trysting first sonnet and begin another (at line 107), it is clear that Juliet is a new kind of sonnet-heroine, audacious and eager for love, not distant and unattainable, like a malicious diva. Cast not as a romantic set-piece, but as an integral part of the dramatic action, this sonnet of Act 1, Scene 5 leads directly into the first quatrain of the second (lines 107-110), broken, ironically, by the arrival of the Nurse. Both sonnets, therefore, unmistakably foreshadow the beginning of true love and its all-too-soon ending by tragic death.