Speaker or Narrator, and Point of View
The speaker uses a first-person limited poınt of view
Form and Meter
English/Shakespearean sonnet using iambic pentameter and a rhyme scheme of ABAB CDCD EFEF GG
Metaphors and Similes
Alliteration and Assonance
Assonance of the "s" sound in "false" and "subtleties"
Assonance of the "oo" sound in "untutored" and youth"
Assonance of "I" sound in "vainly thinking that she thinks"
Alliteration with the words "love" and lies"
Irony
The sonnet is full of situational irony because the reader’s expectations are continually thwarted. For example, on hearing that the speaker’s lover is unfaithful, one expects that speaker will be angry. Instead, he chooses to believe her lies. In fact, the poem describes a relationship entirely built on lies. This sounds negative but the speaker ironically describes this kind of “seeming trust” as the best kind of love.
Genre
Elizabethan poetry
Setting
Tone
Resigned, bemused, embarrassed
Protagonist and Antagonist
The speaker versus his lover
Major Conflict
The speaker's lover constantly lies to him. She swears she is faithful but cheats on him. Similarly, the speaker lies to the lover about his advanced age. Though their relationship is based on lies, lying is also a way of rising above their conflict. They flatter each other in pretending to believe each other's lies.
Climax
The climax in a Shakespearean sonnet occurs at the "volta," a term for the poem's shift in tone or argument at the final couplet. The word "Therefore" marks a summing up of the argument where the speaker admits that they both lie to each other but that this allows them to stay together.
Foreshadowing
Understatement
In describing his old age, the speaker uses the understatement "my days are past the best."
Allusions
“I do believe her, though I know she lies” is sometimes read as an allusion to the Latin phrase “Credo quia absurdum,” which means "I believe because it is absurd.” This phrase, associated with Tertullian's work De Carne Christi, is about Christian belief. The idea is that some of the most difficult aspects of Catholic theology to grasp (the Trinity, for example) are actually opportunities for the faithful to prove their devotion. One believes even if it appears absurd. In the same way, the speaker of Sonnet 138 believes his lover though it is obvious she is lying. This proves his love.
The “false-speaking tongue” is a reference to the serpent who lied to Eve in the Garden of Eden (as written in Genesis). Believing the serpent caused Eve to eat from the Tree of Knowledge, which caused the Fall.
Metonymy and Synecdoche
In the phase "her false-speaking tongue" the lover's tongue is a synecdoche in which represents her entire self and the lies she tells.
Personification
Age is personified in the phrase “age in love, loves not to have years told.” Instead of a person being a certain age, age itself is a person.
Hyperbole
The speaker’s lover describes herself as “made of truth.” It is as if she is so honest that her entire being is made of honesty.