Most love poems say the beloved is always on the speaker's mind. Sonnet 45 goes further and splits the speaker in two. The opening words, "The other two," pick up from the sonnet before it, which mourns that he is too heavy, too much earth and water, to travel to the one he loves. Here the lighter elements take over: "slight air" is his thought, "purging fire" is his desire. Both are "with thee, wherever I abide," so the speaker stays behind as a lesser version of himself.
The poem argues like a doctor. In the old way of thinking, a living body was a blend of four elements. Take away two and the balance fails, so the speaker's "life, being made of four, with two alone / Sinks down to death, oppress'd with melancholy." The line break helps. "Alone" ends line 7, and the sentence drops straight into "Sinks" at the start of line 8, where the stress lands on the verb as if the voice had lost its footing. Elsewhere the language is courtly. Thought and desire travel "in tender embassy of love," like ambassadors carrying messages between two states. By turning abstractions into diplomats, Shakespeare makes them busy, loyal and slightly comic. The oxymoron "present-absent" sums up their odd condition. They are present with the beloved and absent from the speaker, and both facts hurt him.
The sound matches the sense. The poem is in the usual iambic pentameter of a Shakespearean sonnet, rhymed *abab cdcd efef gg*. Line 4, "These present-absent with swift motion slide," is full of soft *s* and *w* sounds, and it does slide. When the messengers return, the diction turns brisk and reassuring: "assur'd," "fair health," "recounting." The rhymes are worth watching too. "Thee" closes lines 6 and 10, the two moments when the messengers go out and when they come back, so the rhyme position keeps returning to the beloved as the messengers do. In line 8, "melancholy" rhymes with "thee" (in Shakespeare's day the final syllable sounded like "ee"), which ties the speaker's sadness to the one he is parted from.
The couplet is where the poem turns. "This told, I joy" gets half a line, and then "but then no longer glad" cuts it off. The happiness is over almost before it is announced. The last line, "I send them back again, and straight grow sad," is all short, plain words, and the word "straight" means *at once*. The mood is bleak because the speaker isn't just a victim of the cycle. *He* sends the messengers away, and he knows that doing so will make him ill. The poem ends with no consolation and no resolution. It stops where it began, ready to run again.
What makes the sonnet significant is how it turns a piece of ordinary science into emotional truth. The four elements were a standard way of explaining bodies and moods, and Shakespeare uses them to make absence feel physical, like a shortage of what the body needs. The conceit is clever, but the cleverness doesn't cool the feeling. The neat logic is what makes the loneliness so hard to escape. Because the poem is built as a closed system with four elements, two journeys and one repeating routine, it suggests that longing is a pattern the speaker keeps living through. Thought and desire are the very things that make a person love, and in this poem they are also what leave him half alive.
Read alongside the sonnet before it, the two poems also work as a pair. The first says that he is held down by heavy matter. The second says that what flies free comes back only to be sent off again. Together they show a speaker who can never be whole while the beloved is away. The poem is witty and quick, but its last line is a quiet admission that he would send his thought and desire out again, however much it costs him.