Sonnet 79 from the 1609 Quarto.

This sonnet is one of a group of poems that deal with the “Rival Poet.” The Fair Youth has had a positive effect, his inspirational beauty lifting the Bard’s poetry to new heights. However, other writers have also been affected by the boy’s beauty, so the poet has acquired rivals who challenge his proprietal claim on the boy.

This sonnet is often paired with Sonnet 78

About Sonnets
A sonnet is a poem which expresses a thought or idea and develops it, often cleverly and wittily.

The sonnet genre is often, although not always, about ideals or hypothetical situations. It reaches back to the Medieval Romances, where a woman is loved and idealised by a worshipping admirer. For example, Sir Philip Sydney in the Astrophil and Stella sonnet sequence wrote in this mode. Poems were circulated within groups of educated intellectuals and they did not necessarily reflect the poet’s true emotions, but were a form of intellectual showing-off. This may not have been true of all; it is a matter of academic debate today. It is generally believed, however, that Shakespeare’s sonnets were autobiographical, though some dispute this.
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Sonnets are made up of fourteen lines, each being ten syllables long. Its rhymes are arranged according to one of the following schemes:

• Italian, where eight lines consisting of two quatrains make up the first section of the sonnet, called an octave. This section will explore a problem or an idea. It is followed by the next section of six lines called a sestet, that forms the ‘answer’ or a counter-view. This style of sonnet is also sometimes called a Petrarchan sonnet.

• English, which comprises three quatrains, making twelve lines in total, followed by a rhyming couplet. They too explore an idea. The ‘answer’ or resolution comes in the final couplet. Shakespeare’s sonnets follow this pattern. Edmund Spenser’s sonnets are a variant.

At the break in the sonnet — in Italian after the first eight lines, in English after twelve lines — there is a ‘turn’ or volta, after which there will be a change or new perspective on the preceding idea.

Language
The metre is iambic pentameter, that is five pairs of stressed and unstressed syllables to the line. The effect is elegant and rhythmic, and conveys an impression of dignity and seriousness. Shakespeare’s sonnets follow this pattern.

Rhyme Scheme
The rhyming pattern comprises three sets of four lines, forming quatrains, followed by a closed rhyming couplet.

In sonnet 79 it forms ABAB, CDCD, EFEF, GG. This is typical of Shakespeare’s compositions.

See Don Paterson – Reading Shakespeare’s Sonnets, Faber & Faber, 2012
Helen Vendler The Art of Shakespeare’s Sonnets Harvard University Press
Shakespeare’s Sonnets with Three Hundred Years of Commentary, Associated University Press 2007
BBC Podcast, Melvyn Bragg, “In Our Time” Shakespeare’s Sonnets