The speaker of "Sonnet 18" is really trying to simplify nature and fate, since he’s trying to hurdle over their limitations with his poetry. One way he does it is to reduce them to economic transactions – something simple, easy to understand, and most importantly, work around.
- Line 4: He describes summer as having a "lease" over the weather. This is, of course, personification, since summer couldn’t hold a lease, but for the purposes of this theme, it’s also a metaphor, since the weather isn’t actually a product that can be bought, sold, or rented.
- Line 10: Here the speaker jumps back into the economics lingo, using both a metaphor and a pun. The metaphor is similar to what we saw in line 4: here beauty, instead of the weather, is what can be bought, sold, and rented. But here there’s also a cool pun with the word "ow’st," as it could mean both "owest" and "ownest." Either way, he’s still playing with the property metaphor, but we can wonder whether the beloved’s beauty is something he or she owns, or something that he or she has only borrowed, and would have to return if not for the speaker’s poetry.