Variety, fluency, and not ungraceful strength are perhaps the chief qualities of Dryden's work, displayed alike in his verse and in his prose. Since he was primarily a poet it is natural to speak first of his verse; and we must begin with a glance at the history of the rimed pentameter couplet, which he carried to the highest point of effectiveness thus far attained. This form had been introduced into English, probably from French, by Chaucer, who used it in many thousand lines of the 'Canterbury Tales.' It was employed to some extent by the Elizabethans, especially in scattered passages of their dramas, and in some poems of the early seventeenth century. Up to that time it generally had a free form, with frequent 'running-on' of the sense from one line to the next and marked irregularity of pauses. The process of developing it into the representative pseudo-classical measure of Dryden and Pope consisted in making the lines, or at least the couplets, generally end-stopt, and in securing a general regular movement, mainly by eliminating pronounced pauses within the line, except for the frequent organic cesura in the middle. This process, like other pseudo-classical tendencies, was furthered by Ben Jonson, who used the couplet in more than half of his non-dramatic verse; but it was especially carried on by the wealthy politician and minor poet Edmund Waller (above, page 164), who for sixty years, from 1623 on, wrote most of his verse (no very great quantity) in the couplet. Dryden and all his contemporaries gave to Waller, rather too unreservedly, the credit of having first perfected the form, that is of first making it (to their taste) pleasingly smooth and regular. The great danger of the couplet thus treated is that of over-great conventionality, as was partly illustrated by Dryden's successor, Pope, who carried Waller's method to the farthest possible limit. Dryden's vigorous instincts largely saved him from this fault; by skilful variations in accents and pauses and by terse forcefulness of expression he gave the couplet firmness as well as smoothness. He employed, also, two other more questionable means of variety, namely, the insertion (not original with him) of occasional Alexandrine lines and of frequent triplets, three lines instead of two riming together. A present-day reader may like the pentameter couplet or may find it frigid and tedious; at any rate Dryden employed it in the larger part of his verse and stamped it unmistakably with the strength of his strong personality.