i.e. (as for instance in Munsarih) when it is reduced to a third of its size.
All these deviations only concern the external shape of a metre and not its rhythmical structure, which does find its expression in the sequence of ‘moving’ and ‘quiescent’ consonants.
The very numerous cases in which this particular sequence in the ancient poems differs from that prescribed by the circles have been covered by a special set of rules. This forms a necessary supplement to the circles, because deviation would be arbitrary __ and thus the circles would loose their authoritative character as Usuul __ if there were no such rules. Just as one is amazed at the regularity of the first part of the system __ the five circles and their normal metres __ so one is confused by the second part with its casuistry and its complications. This , however, is inherent in its very nature. Neither Al-Khalil nor the later prosodists use the term ‘syllable’ , and we can therefore not expect any general rules (e.g. concerning the reduction of long syllables to short , the omission of short syllables etc ). In effect , they were obliged to mention in each individual case whether and to what extent the ‘moving’ and ‘quiescent’ consonants in ancient poetry showed a plus or a minus as compared with the ideal scheme of the circles. This had to be done in every metre and every one of its feet in both halves of the line, and in order to denote them clearly, individual terms had to be created to cover each one of these numerous differences. A certain order and clarity emerges from this baffling list thanks to the fact that all deviations fall into two classes, which perform different functions and appear in different parts of the line.
The last foot of the first hemistich ( al-‘aruud, pl. a‘ariid) and the last foot of the second hemistich ( al-darb, pl. duruub), that is to say, the ends of the two halves of the line, suffer most from deviations.
The terms for these two vulnerable parts of the verse are definite, the terms for the other feet vary and are usually given the collective name al-hashw (‘stuffing’). By analogy, one also distinguishes two groups of deviations, the Zihafat and the ‘Illal. The Zihafaat (‘relaxations’) are, as the name suggests, smaller deviations which occur only in the Hashw parts of the line in which the characteristic rhythm runs strongly, and their effect is a small quantitative change in the weak Asbaab-syllables. As accidental deviations, the Zihafaat have no regular or definite place , they just appear occasionally in the feet. By contrast, there are the ‘Illal (‘diseases’, ‘defects’) which appear only in the last feet of the two halves of the lines, and there, as their name suggests, they cause considerable change as compared to the normal feet. They alter the rhythmic end of the line considerably, and are thus clearly distinct from the Hashw feet. As rhythmically determined deviations, the ‘Ilal do not just appear occasionally but have to appear regularly, always in the same form, and in the same position in all the lines of the poem.
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