Sonnet 18 is devoted to praising a friend or lover, traditionally known as the 'fair youth', the sonnet itself a guarantee that this person's beauty will be sustained. Even death will be silenced because the lines of verse will be read by future generations, when speaker and poet and lover are no more, keeping the fair image alive through the power of verse.

• The opening line is almost a tease, reflecting the speaker's uncertainty as he attempts to compare his lover with a summer's day. The rhetorical question is posed for both speaker and reader and even the metrical stance of this first line is open to conjecture. Is it pure iambic pentameter? This comparison will not be straightforward.

This image of the perfect English summer's day is then surpassed as the second line reveals that the lover is more lovely and more temperate. Lovely is still quite commonly used in England and carries the same meaning (attractive, nice, beautiful) whilst temperate in Shakespeare's time meant gentle-natured, restrained, moderate and composed.

• The second line refers directly to the lover with the use of the second person pronoun Thou, now archaic. As the sonnet progresses however, lines 3 - 8 concentrate on the ups and downs of the weather, and are distanced, taken along on a steady iambic rhythm (except for line 5, see later).

Summer time in England is a hit and miss affair weather-wise. Winds blow, rain clouds gather and before you know where you are, summer has come and gone in a week.The season seems all too short - that's true for today as it was in Shakespeare's time - and people tend to moan when it's too hot, and grumble when it's overcast.

• The speaker is suggesting that for most people, summer will pass all too quickly and they will grow old, as is natural, their beauty fading with the passing of the season.
• Lines 9 - 12 turn the argument for aging on its head. The speaker states with a renewed assurance that 'thy eternal summer shall not fade' and that his lover shall stay fair and even cheat death and Time by becoming eternal.
• Lines 13 - 14 reinforce the idea that the speaker's (the poet's) poem will guarantee the lover remain young, the written word becoming breath, vital energy, ensuring life continues.