I believe he puts usury in the category of crimes against nature because it goes against God’s will in that God said that it’s not from an actual skill and doesn’t provide the world with a good or service.
Why does Dante consider sodomy to be a separate sin from lust?
Sodomy is different from lust in that you actually think about it verses lust is a primal instinct which people can’t help.
Why do you suppose the subdivisions for intellectual sins are much more complex than the sins in upper Hell?
Intellectual sins punishments are worse because they’re actually thought about verses the sins that land you in upper Hell, which are more ingrained into people so that it take a lot of self-control to keep from doing them.
Why make the ninth circle cold when the earlier violent circles were hot?
The ninth circle is cold because it’s the furthest from God, who represents light and warmth.
What part do “threes” play in Dante’s poetic structure and his descriptions of hell?
From: Introduction to The Inferno. Literature of the Western World: The Ancient World
Through the Renaissance. Wilke & Hurt. 2nd ed. Vol. 1. New York: Macmillan, 1988.