The periodic sentence is one way of constructing complex sentences. Its descriptive name is in reference to the punctuation mark — period, or full stop — that designates the end of a declarative sentence. The defining characteristic of the periodic sentence is that its emphatic main point comes at the end.
A complex sentence typically has a main, so-called independent clause and one or more dependent clauses or phrases. A supporting dependent clause can have its own subject noun and predicate verb, and may contain a word that connects it to the independent one. It may or may not be separated by punctuation such as a comma: “The bird soared upward with wind under wing as the sun warmed the air.”
The example sentence of the preceding paragraph is called a loose sentence. It is a straightforwardly understood declaration stating the main point, the independent clause “The bird soared upward,” at the beginning of the sentence. It is sometimes called a continuous style for its linear sequence, or train of thought. Loose sentences employ a literary technique called parataxis, from the Greek word “to place side by side.” They can be thought of as the opposite of periodic sentences.
Hypotaxis means “beneath arrangement,” and a periodic sentence uses this technique of arranging or embedding hierarchical, unequal units of literary constructs. Such a sentence tends to be long, hard to understand, and grammatically incomplete until it all finally resolves with the ending independent clause. The original example sentence can be reworded as follows: “As the sun warmed the air, with wind under wing, the bird soared upward.”
The main point of the sentence comes at the end. The sentence opens with a clause and a phrase without informing the reader to whom or what they refer. With a gradually unfolding succession of differently weighted descriptions, the effective technique is one that can enrich the image, arouse curiosity, or expound an argument. There is an aesthetic of poetry to this way of constructing a sentence — an emotional creation of tension and release. In part due to this extra rhetoric, but also because of a media-influenced cultural preference for brevity, periodic sentences are not commonly encountered.
A periodic sentence can be constructed to excess. Popular among the aristocracy of England in the late 1500s, a literary technique called euphuism employed successive phrases with parallel construction — equal length, grammar, sounds and syllables. A periodic sentence can, however, also be crafted into a more subtle and common, yet effective, variation by introducing a part of the independent clause at the start and concluding the remainder of the main point at the end. “The bird, with wind under wing as the sun warmed the air, soared upward.”