Although the period has not received substantive attention in Shelley criticism, in the classical rhetorical tradition with which he was familiar it was regarded as a foremost element of style, along with tropes, figures, and rhythms—the latter term being sometimes used interchangeably with it. 3 From the Greek periodos meaning" way round,"" circuit," or" cycle," the period is defined by Aristotle as" a sentence that has a beginning and end in itself and a magnitude that can be easily grasped." 4 It is pleasing because it gives the hearer a sense of completion and memorable because it has" number": by its end it rounds off both the meaning and the metrical pattern of the words it comprises. 5 Significantly for Shelley, such rounding is not a coming full circle, the mere repetition of a meaning stated or implied at the beginning, but an arrival at a meaning held in suspense. Aristotle explains that, like a runner in a race with a definite goal," the hearer at every moment thinks he is securing something for himself and that some conclusion has been reached." 6 For this reason Aristotle prefers the period to the" continuous" sentence, which runs on, clause after clause, with no" end in sight." 7 Praising Aristotle's" excellent and apt" definition, Demetrius gives the following example of a periodic sentence from Demosthenes:" Chiefly because I thought it was in the interest of the state for the law to be repealed, but also for the sake of Chabrias' boy, I have agreed to speak to the best of my ability in their support." 8 Although Demetrius, Cicero, Quintilian, and others disagreed with Aristotle on certain points—notably the number of members (or cola) admissible in a period and the relations of length, form, and sound that produced harmony and rhythm—all believed with him that good style was rhythmic and that the flow of its rhythms allowed the hearer to perceive structure. 9 Essential to this structuring was the placement within and between periods of pauses, interruptions of sense and synapheia (continuity of rhythm) originally determined by a speaker's breathing. 10 Quintilian identified two kinds, one appropriate to moments when" our speech should be held up and as it were left in the air," the other to moments when" it should be brought to rest." 11 With the resurgence of interest in rhetoric in late eighteenth-century Britain, partly in response to the scientific psychologies of Bacon and John Locke, definitions of the period were modified to take account