The speaker describes a relationship sustained by gentle, agreed-upon falsehoods. His lover insists she is entirely truthful, and he chooses to believe her—despite knowing better—so she might imagine him a naïve youth, unacquainted with the world’s deceptions. In truth, she knows he is older, and he knows she is unfaithful, yet both suppress these simple facts. He wonders why neither admits the obvious: she does not confess her infidelity, and he does not acknowledge his age. The answer lies in love’s fondness for “seeming trust,” a shared performance of faith. Aging lovers, especially, dislike having their years counted. The final couplet playfully turns “lie” into a pun: they lie together in bed and in words, each flattering the other’s shortcomings through deceit. The mood is warmly ironic—aware of the absurdity, yet tender toward the mutual need that makes the lies feel necessary.
Sonnet 138: When my love swears that she is made of truth — Summary
When my love swears that she is made of truth, I do believe her though I know she lies, That she might think me some untutor'd youth, Unlearned in the world's false subtleties. Thus vainly thinking that she thinks me young, Although she knows my days are past the best, Simply I credit her false-speaking tongue: On both sides thus is simple truth suppressed: But wherefore says she not she is unjust? And wherefore say not I that I am old? O! love's best habit is in seeming trust, And age in love, loves not to have years told: Therefore I lie with her, and she with me, And in our faults by lies we flatter'd be.