“Sonnet 138” explores Truth and Lies in the romantic relationship between a woman and an older man. Her lies are white lies, or flattery, about his age. In the first quatrain, she “swears” (Line 1) that she thinks he is younger than he is. The act of swearing fidelity is itself part of her flattery. In the third quatrain, the speaker wonders why she continues to lie—or be “unjust” and morally questionable (Line 9). His answer is that her lying about his age is a “seeming trust” (Line 11), or a false claim that appears to be true, and is also “love’s best habit” (Line 11), meaning flattery is the best strategy for keeping their love alive. He says, “I know she lies” (Line 2). His awareness of her lies, or flattery, makes him a willing participant. Furthermore, he also lies in telling her that he believes her. This is referenced in the final couplet: “I lie with her and she with me” (Line 13). They are both aware that flattery is part of her seduction of him. He consents to, enjoys, and participates in white lies about his age.

Her flattery offers truths that the speaker and beloved consent to but do not align with external measures of truth.