4. Fá’i.lá.tun, i.e. Watad mafrúk followed by two Sabab khafíf = the Latin Epitritus secundus (-U- -).
The number of the secondary feet increases to six, for as Nos. 2 and 4 contain two Sabab, they “branch out” into two derived feet each, according to both Sabab or only one changing place with regard to the Watad. They are:
5. Fá.’ilun, i.e. Sabab khafíf followed by Watad majmú’= the Latin Creticus (-U-). The primary Fa’ú.lun becomes by transposition Lun.fa’ú. To bring this into conformity with a current derivative of fa’l, the initial Sabab must be made to contain the first letter of the root, and the Watad the two remaining ones in their proper order. Fá is therefore substituted for lun, and ’ilun for fa’ú, forming together the above Fá.’ilun. By similar substitutions, which it would be tedious to specify in each separate case, Mafá.’í.lun becomes:
6. Mus.taf.’ilun, for ’Í.lun.mafá, i.e. two Sabab khafíf, followed by Watad majmú’ = the Latin Epitritus tertius (- -U-), or:
7. Fá.’ilá.tun, for Lun.mafá.’í, i.e. Watad majmú’ between two Sabab khafíf = the Latin Epitritus secundus (-U- -).
8. Mutafá.’ilun (for ’Alatun.mufá, the reversed Mufá.’alatun), i.e. Fásilah followed by Watad majmú’=the Latin Anapaest succeeded by Iambus (UU-U-). The last two secondary feet are transpositions of No. 4, Fá’i.lá.tun, namely:
9. Maf.’ú.látu, for Lá.tun.fá’i, i.e. two Sabab khafíf, followed by Watad mafrúk = the Latin Epitritus quartus (- - -U).
10. Mus.taf’i.lun, for Tun.fá’i.lá, i.e. Watad mafrúk between two Sabab khafíf=the Latin Epitritus tertius (- -U-).[FN#452]
The “branch”-foot Fá.’ilun (No. 5), like its “root” Fa’ú.lun (No. 1), is quinqueliteral. All other feet, primary or secondary, consist necessarily of seven letters, as they contain a triliteral Watad (see supra i. 2) with either two biliteral Sabab khafíf (i. 1) or a quadriliteral Fásilah (i. 3). They are, therefore, called Sabá’í = seven lettered.
iii. The same principle of the Watad taking precedence over Sabab and Fásilah, rules the arrangement of the Arabic metres, which are divided into five circles (Dawáir, pl. of Dáirah), so called for reasons presently to be explained. The first is named: