हेतुहेतुमतोर्लिङ्

The affix लिङ् (Benedictive) is optionally used after those verbs which express the condition and its consequence.
The word हेतु means 'cause' or 'condition' and हेतुमत् means 'consequence or effect'. This supersedes all other tense-affixes; in other words, 'in conditional sentences in which one statement is made to depend upon another as its reason or ground, the Potential is used in both the antecedent and the consequent, otherwise called the protasis (हेतु) and apodosis (हेतुमत्), the former containing the condition or ground of argument, and the latter the conclusion based upon it'. Thus :- दक्षिणेन चेद्यायान्न शकटम् पर्याभवेत् 'if he go by the right side, the cart will not be upset'; यदि कमलकम् आहूयेन्न शकटम् पर्याभवेत् 'if he calls Kamalaka, the cart will not be upset'. Here 'going by the right side' is the protasis (हेतु), and 'not-upsetting' the apodosis (हेतुमत्).

This is an optional use of the Potential; we may use the Second Future in the alternative; thus दक्षिणेन चेद् यास्यति न शकटं पर्याभविष्यति 'if he goes by the south, the cart will not be upset'.

The word विभाषा 'optionally' used in the sutra immediately preceding is also understood here.

Though the anuvritti of लिङ् could have been taken from the last aphorisms, its repetition here is for the sake of pointing out the particular time, namely, the Future, in which the Potential should be employed. Therefore it is not employed in the following sentences: हन्तीति पलायते 'he kills, therefore he flies'; वर्षति इति धावति 'it rains, therefore he runs'.

It, of course, follows that when the non-completion of the action is indicated, the Conditional (लृङ्) should be employed, under these very circumstances. See examples under sutra 3.3.139.