The Inferno has always been the most widely read of the three canticles of the Comedy. Some have suggested that the reason for this is that sin is far more interesting to most people than virtue. In fact the Inferno most likely owes its popularity to the concrete and memorable portraits of some of the individual sinners portrayed in its text: Francesca da Rimini, excusing her adultery with Paolo while being blown about by the winds of passion in Canto 2; Ulysses, describing his mad dash toward Purgatory in Canto 26; Bertran de Born, holding out his severed head like a lantern in Canto 28; Count Ugolino della Gherardesca's account of his slow starvation locked in a tower with his children in Canto 33. These images are depicted permanently on the canvas of Western literature.
Summary
To understand the Inferno beyond this collection of individual portraits, however, it is important, first, to understand its structure. A reader might first expect that the sinners in Hell will be arranged according to the customary medieval hierarchy of the seven deadly sins. But while that arrangement provides the structure of Dante's Purgatory, it is absent from the Inferno. In part this is probably because the convention of the seven deadly sins is a Christian construct, and Hell is outside the church entirely. The organization, therefore, is borrowed from Aristotle's classification of sins in his Nicomachean Ethics. Aristotle's three categories are incontinence (i.e., uncontrolled passion), malice (by which he also implies fraud), and bestiality (probably implying violence). Thus Dante's Hell punishes first those sinners guilty of lust, gluttony, and such lapses of control as are implied by Aristotle's incontinence. Next Dante includes those guilty of violent sins like murder or suicide. Finally, and in the most detail, he describes the various sins involving fraud and malice, ...