(_ββ_) For the reason, then, that words, partly on their own account, as of several syllables, include a number of long and short beats, and in part, although of one syllable, are nevertheless associated with other words, we have thereby to start with a definite, but accidental interchange of various syllables and words without any stable measure. To regulate this accidental relation is just the function of poetry, precisely as it was that of music to define with accuracy the unregulated duration of particular tones by means of the unity of time-measure. Poetry therefore establishes specific combinations of long and short syllables as the law, by virtue of which, under the aspect of _time-duration,_ it has to arrange the series of syllables. What we therefore get in the first instance are the different successions of time. The simplest is the mutual relation of pure equality, as, for example, we find it in the dactyl and anapaest, in which the two short syllables may coalesce according to definite rule in two long syllables (the spondee). Secondly, a long syllable may be placed next one short; in that case we have a profounder distinction of derivation, though under its simplest form. Such are the iambus and the trochee. We find a more complicated combination, when a short syllable is interposed between two long ones, or one short precedes two long, as in the cretic and bacchius. (_γγ_) Such _isolated_ time-relations would, however, open the door to unregulated contingency if they were permitted to follow one another anyhow in their motley differences. In fact the entire aim of such regulation would vanish under such conditions, in other words the regulated series of long and short syllables. From another point of view we should wholly fail to secure a definite beginning, conclusion, and central position, so that the caprice which here once again asserted itself would entirely contradict that which we previously established, when considering musical time-measure and beat, as to the relation in which the percipient ego stood to the duration of tones. In other words, the ego requires a combination on its own account,[20] a return out of the continuous forward movement in time; and only seizes on the same in virtue of definite unities of time and their, as such, emphasized commencement,[21] regulated in their entire series and terminations. This is the reason why, in the _third_ place, poetry also sets out the particular time-relations in a series of _verse-lines,_[22] which in respect to the type and number of their feet, no less than in that of their commencement, progress, and conclusion, are subject to rule. The iambic trimeter, for instance, consists of six iambic feet, of which any two constitute an iambic dipody. The hexameter consists of six dactyls, which again, in certain positions, may coalesce in spondees.