The Bedford Glossary of Critical and Literary Terms - Ross Murfin 2018
periodic sentence: A complex sentence that is not syntactically complete until its very end; the opposite of a loose sentence, in which an independent clause is followed by one or more independent or dependent clauses. A periodic sentence includes at least one dependent clause and/or parallel construction (and often several of each) before the final independent clause, which completes the sentence and provides its grammatical close as well as its meaning. Periodic sentences are comparatively formal and are often used to heighten suspense by deferring the main point until the last word. Works predominantly containing periodic sentences usually exhibit hypotactic style.
EXAMPLES: The following sentence from Jonathan Swift’s Gulliver’s Travels (1726) is periodic:
And it must be confessed, that from the great intercourse of trade and commerce between both realms, from the continual reception of exiles, which is mutual among them, and from the custom in each empire to send their young nobility and richer gentry to the other, in order to polish themselves, by seeing the world, and understanding men and manners, there are few persons of distinction, or merchants, or seamen, who dwell in the maritime parts, but what can hold conversation in both tongues.
So is this sentence from John Stuart Mill’s On Liberty (1859):
If all mankind, minus one, were of one opinion, and only one person were of the contrary opinion, mankind would be no more justified in silencing that one person than he, if he had the power, would be justified in silencing mankind.