Time,the temporal state of life, is often treated by Shakespeare as the invidious tyrant or as a fickle force in contrast to the everlasting condition of the spiritual. Certainly, time, the transience of life and the deceptive power of beauty are recurring themes in the sonnets.
About the tyrant Time, Shakespeare writes in Sonnet CXXIV,
If my dear love were but the child of state,
It might for Fortune's bastard be unfather'd,
As subject to Time's love, or to Time's hate,....
Regarding the deception of beauty, Shakespeare writes of the eyes perceiving beauty in Sonnet CXXXVII,
They know what beauty is, see where it lies,
Yet what the best is, take the worst to be.
If eyes, corrupt by over-partial looks,....
You can find these two elements considered together in several of his sonnets. I immediately thought of Sonnet #73 "That time of year thou mayst in me behold."
In this poem, the speaker is commenting on the passage of time in the course of his life. Shakespeare employs the "year of life" metaphor here as the speaker comments that "thou mayst in me behold when yellow leaves, or none, or few do hang upon those boughs." This image is suggesting that the man is the "fall" of his life, old, near the end (which is symbolized by winter) but still alive. The image of a almost bare, yellow-leafed tree is in contrast to the beauty of a tree in the prime of summer -- green, full and vibrant. Time has passed and the glory as faded.
Later in the poem the speaker says, "In me thou see'st the glowing of such fire that on the ashes of his youth doth lie." Here the passage of time and failing of beauty is compared to a fire. In youth, there are glowing flames and significant heat, but the passage of time has dimished the fire to ashes, and ironically, those ashes are suffocating the fire itself. Again, time is destroying beauty.
Time could very well be the most pervasive theme, one that runs throughout all of the sonnets. In order to consider such a broad topic, you should understand that, by most scholars, the sonnets are considered to fall into two groups.
There sonnets are considered to be addressed to a "young friend," and, as relates to time, are encouraging this friend to marry so that his beauty may carry on in his children. And there are sonnets considered to be addressed to a "dark lady," a mysterious figure that the poet appears to love, but have mixed feelings about as well.
Time is used throughout the sonnets as an enemy to be defeated, and one way the poet determines to defeat time is through writing and leaving a written legacy behind. In essence, he may not live forever, but his words shall.
Beauty is seen as related to time, in that it fades with age. The poet does take on this theme throughout the sonnets, but again, his consideration of beauty is different with the different persons he is addressing. When he addresses the "young friend," he does extol his beauty, but doesn't really ever describe it in detail. With the poems written to the "dark lady," he spends much language on description of her beauty -- language that is often times satirical and disdainful.
Time and Beauty are important themes in the sonnets, their uses often bearing direct relationship to whom the poet is addressing the specific sonnet.
In his sonnets, Shakespeare portrays time as a destructive force that seeks to whittle away the beauty of people, objects, and events. However, he says that true beauty may outlast time and gain a sense of immortality. For example, in Sonnet 55 "Not marble nor the gilded monuments," the speaker says that although time seeks to destroy the beauty of the world, the poet may capture this beauty in the lines of the poem, thus allowing beauty to outlast the destructive nature of time. In the poem's envoi, the speaker says, "You live in this, and dwell in lovers' eyes" to suggest the sense of immortal beauty.