In the first line of sonnet 152, the speaker commits the grammatical sin of a dangling participle: “In loving thee thou know’st I am forsworn”—the prepositional modifying phrase “in loving thee” requires that element modified be “thou.” Of course, that makes no sense. The speaker is not saying that the addressee, the dark lady, is loving herself.
The proper modified element is, of course, “I” which appears in the clause “I am forsworn.” The grammatical constructions of this poet are nearly pristine in their correct usage. He, no doubt, is relying on the second line to clear up the misunderstanding that his dangling participle causes.
First Quatrain: “In loving thee thou know’st I am forsworn”
As he has done many times before, the speaker resorts to legal terminology as he continues winding up his artistic study of his relationship with the dark lady. He reminds her that she already knows he has sworn to love her, but then he adds a paradoxical, “But thou art twice forsworn, to me love swearing.” She broke her vow to be sexually faithful by bedding other men, and then she broke her vow to love him by telling him she hates him.
Second Quatrain: “But why of two oaths’ breach do I accuse thee”
The speaker then poses the question, why should I blame you for breaking two vows when I break twenty? He claims that he is “perjur’d most” or that he has told more lies than she has. He claims that on the one hand, he makes his vows only to “misuse thee.” Yet on the other, all the faith he has in her “is lost.”
Third Quatrain: “For I have sworn deep oaths of thy deep kindness”
It turns out that the speaker’s “oaths” held the noble purpose of giving the woman all those qualities that she lacks: love, truth, constancy. He has attempted repeatedly to elicit from her “deep kindness” all of these noble qualities. By showing her how to trust, he had hoped she would become trustworthy.
In addition, he had hoped to enlighten her by opening her eyes to more decent ways of behaving, but he ultimately found himself lying to himself, trying to convince his own eyes that what they saw was false, that he pretended for the sake of his misplaced affection for this woman.
The Couplet: “For I have sworn thee fair; more perjur’d I”
The speaker has many times declared that the woman was “fair,” and he now admits that such swearing made him a liar. He committed perjury against truth by swearing to “so foul a lie.” The conclusion of the relationship is achieved through the implied finality of the legalese that denounces for the last time the source of falsehood and treachery.
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