Ironically, the presence of this couplet at the end of the poem suggests that the speaker is defensive about his argument. He challenges the reader’s doubt in his claim to strike down the counterclaim before it can arise. However, because this occurs in the couplet, this counterclaim actually works to undermine his claim. It leaves the reader with the idea of the counterclaim rather than the idea of the original argument and it serves as a weak defensive argument rather than one based on strong logic.

The use of “loved” in the past tense undermines the speaker’s own model of love. According to his views, love is eternal and “not Time’s fool.” By hinging his argument for timeless love on the existence of men who have “loved”—suggesting that love is time-bound—he weakens his own claim.

“I never writ, nor no man ever loved” are two obviously absurd claims. People have loved throughout history and the existence of the text alone proves that the speaker has “writ.” By presenting these objectively undeniable claims, the speaker tries to make his claims about love similarly undeniable. Ironically, this rhetorical movement weakens his claim.

The religious theme the speaker introduces in the first quatrain is reiterated here. Ideal love, not subject to the fickleness of time, lasts until “the edge of doom.” “Doom” here alludes to the biblical conception of Last Judgment, the point where time ends and all human souls are judged by God. The speaker’s implicit claim is that his idealized model of love will be well-judged by God.

“I never writ” is ironic here because it takes place in a printed sonnet. The very fact that the reader is reading these lines proves the speaker’s point: I have written therefore my description of love is true. The sonnet’s placement in the sequence bolsters the strength of the phrase. If the reader has read 116 sonnets, it is clear that the speaker “has writ.”

“Upon me proved” inserts the speaker and his beloved into the poem. While the three preceding quatrains discussed love as an abstract concept, this final assertion involves proving the “error” of his logic using the speaker’s relationship. This final point implies that the speaker’s love for the youth is this idealized “marriage of true minds”—only by showing error in this relationship could one disprove the argument of this poem.

The word “shaken” ends the line with a feminine rhyme, a multisyllabic word that ends on an unstressed syllable. This weakens the meter. In the case of the word “shaken,” form and content come together. The implied image, after all, is that of a shaken ship.

The exclamation “O no!” also defines a tonal shift. The first quatrain is mired in dry, legal language. The second and third quatrains, by contrast, depict stars, storms, ships at sea, Father Time’s sickle, and Doomsday. As he transitions into a positive definition of love, the imagery becomes lively, the tone romantic.

“Proved” returns to the legal language of the first quatrain. This marks a tonal shift back to the stark, black and white logic that we saw at the beginning of the poem. While the middle of the poem explores romantic images and sentiments, the end offers a final, concrete point that asserts the speaker’s claim.

This line further criticizes the attempts lovers make to change their beloveds. The word “bends” suggests that the desire to “remove” is metaphorically crooked. The remover—the false lover—“bends” to a lower state of morality.

While the last quatrain marked a shift from negation to definition, this quatrain begins with the speaker returning to the rhetorical movement of the first quatrain in these last two lines: he is once again describing ideal love by comparing it against physical love. The implication of this line is that ideal love is not subject to time’s sickle while physical love is by nature Time’s fool.

The first quatrain contains three phrases in which a word is repeated: “love is not love,” “alters when it alteration finds,” and “remover to remove.” This mirroring effect imitates the dance of the couple. That the paired words often appear in slightly varied forms—such as “alter” and “alteration”—reinforces the theme of alteration. The words, like the lovers they imitate, exist in a state of tension because of their differences.

The “bending sickle” in this line recalls the image of Father Time present throughout the sonnet sequence. This metaphor equates time with the image of the grim reaper, or death itself. With this imagery the speaker is suggesting that erotic love based on youth and beauty is temporal and subject to physical death.

“Love is not love” also alludes to a famous biblical episode in which Moses requests God’s name. God replies, “I am that I am” (Exodus 3:14). The negative logic of “Love is not love” suggests that the non-ideal love the speaker defines is unholy. This spiritual context becomes important in the final quatrain.

“Rosy lips and cheeks” can also be read as an allusion to Cupid, the childlike, winged god of love. Cupid is the god of desire, erotic love, and attraction. In this metaphor, the speaker distinguishes his love, the marriage of true minds, from this ephemeral physical love. He does this to assert that his love is everlasting, not subject to time’s “sickle” as physical attraction is.

“Rosy lips and cheeks” is metaphor that evokes temporal youth and beauty. Like the flower that dies in winter, youth and beauty are ephemeral, subject to the ravages of time.

“Worth’s unknown” can be read as a positive or negative characterization of this love. It could be read as “unknown” because it defies the boundaries of physical restraints, such as measurement and human language. However, it could also be read as “unknown” because it is unattainable: no one has ever achieved this ideal love, this “mark,” and thus no one knows what it is.

The phrase “Love is not love” further emphasizes the separation between platonic and erotic love. To the speaker, capital-L “Love” refers to his ideal model of love, a platonic meeting of “true minds.” On the other hand, “love” with a lower-case “l” is erotic, fickle, and always seeking change.

The sonnet’s opening lines draw from the language of the marriage ceremony in the Book of Common Prayer, which discusses the “union of true minds” as well as the declaration of “any impediment why they may not be coupled together.” The speaker’s use of this language gives the opening quatrain a legalese tone.

“Height be taken” refers to a navigation tool in which seafarers would measure the height of the pole-star and calculate their latitude. This allusion read in conjunction with “whose worth’s unknown” suggests a distinction between physical and figurative measurements: while the height of the star can be calculated, its actual distance is boundless. The star is therefore metaphorically beyond worth, beyond calculation; it exists outside physical systems that could give it a relative value.

The speaker sets the stage by defining the type of love he idealizes: the “marriage of true minds.” This marriage is a platonic relationship. “Mind” evokes the cartesian duality of mind versus body; the emphasis on the former suggests a nonsexual union.

By “wand’ring bark” the speaker means a ship on the sea using the stars as tools for navigation. The second quatrain uses these navigation metaphors to portray the Love (which consists of a marriage between true minds) as guiding all other types of love.

Depicting this love as a “fixed mark” paints it as an objective or goal for all lovers. While the first quatrain fluctuates back and forth between parallel words and the grey areas between their differences—alters/alteration, remover/remove— “fixed mark” represents the singular nature of this love. The speaker is now defining the stable marriage of two minds rather than fickle physical love.

“O no” marks a rhetorical shift in the poem. While the first quatrain focused on the fluctuating features of variable physical love, this second quatrain focuses on the concrete nature of real love. The speaker transitions from defining the love by what it is not to defining the love by what it is.