What are the key themes in the poems "Roscoe Purkaphile" and "Mrs. Purkaphile?"

The major theme in these poems is the commitment of marriage. Roscoe Purkaphile was never keen on the idea of being married, but eventually resigned himself to it. Mrs. Purkaphile, however, took her vows very seriously: "But a promise is a promise / And marriage is marriage...". The seriousness of her dedication is highlighted by the fact that she is not known by her first name, but only by her husband's surname. She is a woman who is dedicated to tradition.

Roscoe, on the other hand, comes off as a man who is constricted by social convention. He wants to "escape" from Mrs. Purkaphile. He hopes that she will divorce him, or that she will die before him so that he can be free again. He concludes, however: "But few die, none resign." Not many young women die suddenly; and none will risk the social opprobrium that comes with divorce. So, he becomes an unfaithful liar: "Then I ran away and was gone a year on a lark...I told her that while taking a row in a boat / I had been captured near Van Buren Street / By pirates on Lake Michigan..."

Mrs. Purkaphile knows better, but chooses to believe his lie so that she can keep their marriage intact. She knows that he is having an affair: "I knew very well / What he was doing, and that he met / The milliner, Mrs. Williams, now and then..." It is not out of respect for her husband, but "for [her] own character" that she refuses to divorce. She made a promise; marriage is a vow for life. If she cannot keep this promise, then she is not true. She contrasts her own character with her husband's: "I refused to be drawn into a divorce / By the scheme of a husband who had merely grown tired / Of his marital vow and duty." She trivializes his feelings with the phrase "merely grown tired," and asserts her own moral superiority. 

Though marriage is the main, overarching theme, there are also the peripheral themes of infidelity, morality, existential boredom (Roscoe wants to be with other women because people often grow bored living with the same person), and the place of God in marriage. Much of what Mrs. Purkaphile believes about marriage is probably rooted in religious faith. Ironically, Roscoe comes to agree with her side of things: "I then concluded our marriage / Was a divine dispensation / And could not be dissolved, / Except by death. / I was right." Due to his wife's earnestness, only death allowed them to part.