Because the hero of the Inferno is also the writer, we have to look at both aspects of him, Dante the author and Dante the character.
Mainly, the difference between author-Dante and character-Dante is that author-Dante writes to us from the future. He can be identified as the real-life Dante, having already (allegedly) experienced Hell and now reflecting on his life-changing experience.
One way we can tell author-Dante apart from character-Dante is that the former drops hints about things that will happen to his character self. And all of the sinners' prophecies just happens to come true. Of course, what’s considered "prophecy" to character-Dante is history to author-Dante. Basically, we can look at author-Dante as a more mature and slightly jaded version of character-Dante.
Whenever discussing his own writing, author-Dante speaks very highly of himself. He begins throwing around his weight, comparing himself to the old masters of poetry and often finding himself superior. Of course we must take into account that he is talking about his own poetry and might be slightly biased. But, skeptical reader, Dante has every right to brag. He’s just good at what he does. Not only is he writing about a larger-than-life topic which nobody has addressed before (Hell and the other divine realms), but he does it in a language that’s decidedly not Church Latin. While he throws in all the fancy tricks that scholars love, he writes on a level that the common Italian person can understand. In other words, Dante writes in a conversational style. Translators often ignore this, preferring instead the lofty coattails-and-cumberbund tone of…say…Virgil.
Let’s just say it: Dante’s kind of a softie. At least in the first half of the Inferno. We understand that going for a stroll in Hell can be traumatic. Dante passes out from pity twice in the first six cantos. And we’ve lost count of how many times he breaks into tears. But you have to admit that Dante’s got heart. Perhaps we can understand his sympathy for the first few sinners like Francesca or Ciacco. But Ugolino? He watched his children die and then possibly ate them.
Empathy is one of Dante’s greatest attributes. Compassion is his cup o’ tea and he can see the deep pathos in each punishment as well as the need-for-love part of every sinner’s black soul. In Hell, of course, such a forgiving viewpoint is bound to go astray.
Virgil does make Dante toughen up a little as they go on. In reality, he doesn’t have much to do. Dante picks up the tough guy vibe pretty quickly, raging at Filippo Argenti, arguing with Farinata, ranting against Pope Nicholas III, threatening Bocca with violence, and even breaking a promise to Fra Alberigo. After each round of righteous indignation, Virgil claps Dante on the back and congratulates him for putting yet another sinner in his place. Thus, Dante is learning to slam the sinners and quash his natural sense of pity.
But wait a second. Doesn’t the act of calling "rudeness…a courtesy" sound vaguely familiar? Like "chang[ing] a no to a yes"? In condemning the sinners, Dante may be participating in the very crimes he denounces. Like giving into wrath by pushing Filippo off the boat, and turning against his fellow Florentine Bocca just as Bocca betrayed his troops.
The big revelation is that Dante is human, not some holier-than-thou spirit. He, too, is capable of sin. When worked up, Dante can lose it with the most wrathful of the Wrathful and mess with words’ meanings just like those filthy falsifiers. The only difference is that Dante is doing it for the love of God, against people already judged as evil.
Whether or not these complications really make a difference may be a moot point. But if you’ve noticed, our hero has gone from a bleeding-heart Dante to Dante the punisher. Polar opposites, but both sinful in their own way; first, Dante’s hasty pity shows a weakness of judgment and later, Dante’s damning rhetoric is kind of hypocritical.
Our dynamic duo. Virgil and Dante. Dante holds an awful lot of admiration for Virgil. He expresses this in water imagery – it’s an unusual way to show love, but hey, he’s a poet. His very first words to Virgil compare him to a "fountain / that freely pours so rich a stream of speech" and later he calls Virgil "the sea of all good sense." Dante paints this wonderful image of knowledge and learning that can flow from one source to the other and, thus, is open to anyone who makes the effort to unlock the dam. But all metaphors aside, both share an earnest mutual respect.
The two have a great deal in common. Both are epic poets. Both come from the boot-shaped peninsula now called Italy. Both are very concerned with the meaning of piety. So they have lots to talk about. Dante plays the role of a good student – asking questions, listening to sinners’ stories, and imitating Virgil. Virgil acts the part of the sage professor, while Dante’s your typical overachiever.
Except all is not well in the Academy of Poets. Dante learns at light speed and Virgil makes the mistake of…well…failing at the gates of Dis. So after Canto IX, Dante begins sassing off to Virgil. It happens in Canto XI, then again in Canto XXVI, and also in Canto XXIX. You get the idea. He’s not rude, but his "yes, sensei" attitude is gone. Along with his parallel development of the habit of blasting sinners instead of crying with them, Dante is gaining confidence in the words exchanged with Virgil. However, Dante’s cockiness towards his teacher seems to do both men good, because they slowly grow more open in calling out each other’s faults or lapses of judgment.
By the end, it’s clear that Virgil still has the greater encyclopedic memory than Dante, but Dante student has learned a lot. Might there be reason to suspect that he surpasses his master morally?