As Canto XVIII begins, Dante thinks to ask Virgil another question but holds back. Yet Virgil anticipates his curiosity and prods him to ask. Dante hopes he’ll further explain this love. Virgil says that the mind is “disposed to love at its creation” and that, after forming mental images from “real forms,” it will become inclined to that thing in natural love. These natural inclinations rise “as fire” towards love of God, “where matter lives the longest.” Yet Dante wonders how this love could result in sin, if desire is natural and uncontrollable. Virgil explains that while desire may not be controlled, one can refrain from acting on one's desires. This ability to refrain, he says, is free will.
Suddenly, “a throng” of runners rush past them: these are the slothful, now made to run continually in a vigorous sprint. One mentions Mary, and another mentions Caesar. Virgil asks for assistance, and one penitent, the Abbot of San Zeno, introduces himself and runs forward. Two others, straggling behind, mention the Israelites who died in the wilderness and the Trojans who failed to obtain glory with Aeneas. At this point, Dante falls asleep.
As dawn approaches, Dante dreams of a woman approaching him; she is “stammering, cross-eyed, splayfooted, / with crippled hands and sick pale complexion.” Yet when he looks at her, she begins to speak and becomes beautiful. She sings, revealing herself to be a siren. But another, “holy” woman appears next to Dante; Virgil, too, appears and seizes the siren’s clothing. This “exposed her belly” and a foul stench that wakes Dante up. Virgil prods him to continue ascending, though Dante is still burdened by the dream. As they climb to the next terrace, Virgil asks why he seems so distracted. When Dante replies, Virgil tells him that he has seen “that ancient witch / who alone is purged with tears above us here” and refuses to give more information.
Dante is reinvigorated, and they reach the next terrace. On it, Dante sees people “lying face down on the ground and weeping.” After Virgil asks for guidance, he consents to have Dante further question the soul who responded. In Latin, the soul reveals that he was the successor Petri or the successor of Peter: this is Pope Adrian V. Though he died early in his reign, he is still marked by the avarice of the Papacy and the church, and so we learn that this terrace punishes the avaricious. When Dante kneels beside him in reverence, Adrian asks that he “go his way.”
Dante, unable to stand against Adrian’s “worthier will,” moves forward, although “the sponge” of his curiosity is “not full yet.” Dante bemoans the “age-old wolf” of avarice and hears, among the weeping, examples of generosity: Mary, Fabricius, and Saint Nicholas. After Dante asks which soul has just mentioned these examples, he learns that this penitent is Hugh Capet, once king of France. Hugh tells of the sins his sons will commit and their lust for power. He predicts that a Charles from France will “acquire, not land, / but sin and shame.” He sees, in the future, a “new Pilate” and wonders when God will exact vengeance on these sinners. His dialogue continues; he explains that at night, they must remember examples of avarice: Pygmalion, Midas, Achan, Sapphira, Polymnestor, and Crassus. All of the penitents here must give “voice to goodness,” though some speak louder or softer; and with this, Hugh Capet asserts that he was not speaking alone.
Dante and Virgil continue on, when suddenly an earthquake shakes Mount Purgatory; Dante feels “a chill, / like the chill of death,” but soon voices are singing Gloria in excelsis Deo. The two pilgrims stand still until both the earthquake and singing stop. As they continue, Dante is disturbed by not being able to understand what has happened.
As Dante wonders about the earthquake, a figure appears next to him as suddenly, as Christ did to Luke after the resurrection. The three talk, explaining again Dante and Virgil’s reasons for being in Purgatory. Virgil notes Dante’s continued curiosity and asks about the earthquake. The shade reveals that he had just finished his 500-year punishment and is now ascending the mountain: when any penitent finishes, the mountain quakes and "Gloria" is sung. When asked, he reveals that he is Statius, a Latin poet, admirer of Virgil, and one of Dante’s influences. He says the Aeneid was his “mamma” and “nurse” and praises Virgil. Dante wryly smiles at the irony of the situation, and with Virgil’s reluctant consent, reveals Virgil’s identity, to Statius’ joy.
In Canto XVIII, Dante develops the discourse on love initiated in the last canto. Virgil’s description reveals how he was influenced by Aristotle and Plato, both of whom were taken up by medieval philosophers, who were often Christian and neo-Platonist in disposition. In Plato’s Symposium, Socrates suggests that desire leads people up a “ladder of love,” ascending from earthly things to the love of philosophy, which is focused on ideal forms as opposed to earthly love. Virgil’s simile, describing love like fire, which naturally rises upward, cements this influence.
Of similar importance is Virgil’s definition of free will. Rather than being positive free will (the capacity to choose), free will in the Commedia is seen as negative: it can choose not to do something. This definition helps to resolve a number of theological problems and shows how Dante is considering theological issues as he develops his poem.
Although it’s not entirely clear what she represents, the woman in Dante’s dream has produced an immense amount of criticism. It is clear, admittedly, that she represents some form of temptation and sin; she might have even influenced Milton’s depiction of Sin as a woman with a gnarled belly in Paradise Lost. It seems likely that she represents the temptations of the flesh, especially erotic love. In contrast to the “platonic” love between Beatrice and Dante, the attraction between Dante and this woman is largely focused on her body and voice. Further, because this dream follows immediately on a number of cantos focused on “Divine Love,” Dante subtly suggests his own difficulties with love and controlling his will. In juxtaposition to the dream of his weakened will, Pope Adrian V demonstrates a strong will, focused on penitence.
Once again, Dante shows how his separate canticles (books) of the Commedia link up. When he refers to the “age-old wolf” of avarice, he gestures back to Inferno II, where a wolf appears to menace Dante, stopping his ascent. Yet the twentieth canto also looks forward, quite literally. Hugh Capet’s prediction comments on events that had occurred by the time Dante the poet wrote the Commedia, but before the time when Dante the pilgrim descends to Hell. This is how the later cantos of the Purgatorio will develop “prophecies.”
Canto XXI is largely focused on poetry itself, but it also links poetry to the women of the Commedia. When he describes the Aeneid as his “mamma,” Statius uses an Italian vernacular term which emphasizes the Aeneid as both a nurturing force and as specifically an Italian kind of poetry. We can then see some of Dante in Statius: both turn to Virgil’s poetry as a nurturing and guiding force.