Some examples are available. See selected texts Pro Archia 3.5 and Divinatio in Quintum Caecilium 1.1
A period is difficult to define accurately and comprehensively. In fact, there is disagreement in both the modern and ancient literature about what a period is.
Quintilian IX iv provides a useful starting place. He distinguishes (IX iv 19-22) two kinds of style: vincta atque contexta ("tightly woven") and soluta ("loosely woven"). The period, along with the comma ("phrase") and colon ("clause"), is characteristic of the tightly woven style (these terms are defined by Quintilian at IX iv 122ff). He also distinguishes two kinds of periods:
Both types require at least two elements, the difference being that in the simple period a single thought (or proposition) is brought around to its close through a structure of suspense and anticipation, while in the complex period different thoughts or propositions are so arranged that they come to a well-rounded close.
We will be especially interested in the complex rhetorical period. A strict definition would insist that the complex thought be so arranged in cola ("clauses") and commata that the whole is brought to a close simultaneously with the end of the formal grammatical structure of the period. Furthermore, the thought should not appear to be merely additive, with not overarching structure of suspense and expectation. The simplest way to achieve this kind of closure is to put the main verb last.
But this is by no means the only way to create a tight or rhetorically effective period. In practice, aesthetic concerns (rhythm and balance), idiomatic concerns (that sense we all have that yet another shoe is going to drop), and logical concerns (the grammatical structure may seem to be complete, but surely there is something more to say) create any number of possible structures for tight or loose periods.
The most important aspects of the complex rhetorical period are as follows:
- It contains more than one proposition.
- A simple sentence can be rounded off through two commata and be periodic, but it will not be a complex period.
- A sentence with only one main verb may be periodic, if there are subordinate structures that contain in themselves a proposition: subordinate clauses, predicative participles, even appositional structures that offer a proposition. Predicative modification offers fertile ground for the insertion of a second proposition within the main proposition.
- A periodic sentence is necessarily a complex thought and therefore is better suited to some kinds of discourse than others, to some parts of the speech (exordium, peroratio) than others (narratio)
- Complex thought and formal sentence closure are simultaneous. That is, the audience must expect the sentence to continue even when the first proposition has been stated. This entails various devices which create suspence and anticipation while postponing formal closure.
- Periodicity is fairly well assured if the subordinate clause comes first: Qui legit, paedicat.
- Whenever the main verb is last, formal sentence closure will necessarily be postponed until the end of the sentence. While this is a common position for the main verb, it is by no means the rule.
- If the main verb comes first, then, there must be some signal that the sentence will continue after the main clause: typically, an anticipatory demonstrative or a correlative.
Ille vir beatus videbatur qui…
Tantum qaudebatur quantum…
- A sentence with two main verbs must rely upon devices of suspense and foreshadowing if the audience is to understand that the thought is not complete when the first main clause is over.
- The simplest and perhaps most common way to prevent a sense of closure at the end of the first main clause is to use anticipatory structures: et… et…; nec… nec…
- Whenever the audience expects the thought to continue beyond the formal close of the first main clause, there will be periodicity. An author may sometimes depend upon idiom, rhythm, aesthetic balance, or common sense to create suspence.
veni, vidi, vici
odierint, dum metuant.
- The considerations outlined above lead to the conclusion that, if a sentence continues beyond its formal closure and begins to add propositions which are in no way (neither in content nor in form) anticipated, the sentence ceases to be periodic in the strict sense.