प्लुतावैच इदुतौ

In forming the प्लुत of the diphthongs s ए and ओ , their last element इ and उ get the प्लुत।
The pluta ordained by 8.2.84 &c. when applied to ऐ or औ, cause the prolation of the last element of these diphthongs namely of इ or उ ॥ The word प्लुतौ in the sutra is Nominative dual of प्लुत, and the aphorism literally means "इ and उ are pluta of the diphthongs ऐ and औ" ॥

Thus ऐ३तिकायन, औ३पगव ॥

The letters ऐ and औ are compound letters or diphthongs consisting of अ + इ and अ + उ ॥ In making the pluta of these, the question arises, should both अ and इ (or उ) be prolated, or only the last element, or the first only. The present sutra answers that doubt. If in the analysis of these letters, अ be taken as having one matra (or moras), and इ and उ one matra, then the pluta इ and उ will have two matras, so that the whole pluta ऐ and औ will have three matras. In fact, the word प्लुत is used here as a Past Participle of प्लु, having the force of a verb; and इदुतौ प्लुतौ means इदुतौ प्लवेते i.e. वृद्धिं गच्छतः, i.e. इ and उ are lengthened. And इ and उ are lengthened to that extent, so as to make ऐ and औ of three matras. Thus when अ + इ and अ + उ each has one matra, then the pluta of इ and उ will have two matras as we have said before. But when अ + इ (ए) and अ + उ (ओ) are considered to have अ half matra, and इ and उ one matra and a half, then इ and उ are made pluta, so as to have two and a half (2 1/2)matras each, thus the whole of ऐ and औ, has still three matras. In fact, the definition of pluta is, that it is a vowel which has three matras: so that we should so prolate the vowel as to make it have three matras.

But according to Patanjali, this pluta of ऐ and औ has four matras. Thus अ + इ and अ + उ each has one matra. The pluta of इ and उ will have three matras. Thus अ + इ३ and अ + उ३. or the whole has four matras. According to this view a vowel may have four matras also.