Naming one thing by another that is connected to it: the part for the whole, the object for its owner, the place for its people, the cause for the effect.
In Purgatory
Rome, which made the good world, used to have two suns, which let one see both paths, the world's and God's. One extinguished the other; and the sword was joined to the crozier, and the one with the other, joined together by living force, necessarily go astray.
"The sword" and "the crozier" name the power of the emperor and of the pope by the objects that symbolize them. The exchange spares the names and lets one see that what has joined is the function, not the person.
Cantos XIII to XVI: Envy and wrath, Marco Lombardo, to Dante, on Rome's two powers
for a month and a little more I tasted how heavy the great mantle is to one who guards it from the mud, so that all other burdens seem feathers.
do not wait any longer for my word or my nod; free, upright and sound is your free will, and it would be an error not to act according to its desire: therefore I crown and mitre you over yourself.
Cantos XXVI to XXIX: The fire and Eden, Virgil, to Dante, in his last speech before falling silent
Subscription
The explanation of each passage, in every device and in every work, comes with a subscription.