सम्भावनेऽलमिति चेत् सिद्धाप्रयोगे

The affix लिङ् (Benedictive) is used after a root, when the expectation (of a person or thing being able or competent to do or suffer the action denoted by the verb is implied (or expressed by any other word used along with them) than 'alarm'.
The word लिङ् is understood here. The word सम्भावन means supposition and expectation in the power or ability of another to perform any action. This word is here qualified by the sense of the word अलं. The word अलं means 'adequate'; so that the above-mentioned सम्भावनं must be completed, full and true i.e. realised. The phrase सिद्धाप्रयोगे qualifies अलं, and means 'if the non-employment or omission of अलं is valid or unobjectionable. When is that unobjectionable, when the sense of अलं is implied by the sentence, but this word itself is not used? The Potential Mood is employed when the expectation is of the kind above described. This rule debars all other tense-affixes. Thus अपि पर्वतं शिरसा भिन्द्यात् 'l expect he will break even the hill with his head'; अपि द्रोणपाकं भुञ्जीत 'I expect you will eat away even a drona of cooked food'.

Why do we use the word अलं 'competent to do'? Observe, विदेशस्थायी देवदत्त प्रायेण गमिष्यति ग्रामम् 'I expect Devadatta who is living in a foreign country, will some day go back to his country'. Here though 'expectation' is expressed the idea conveyed by अलं, namely, the power to do something or adequacy to do is not present; and hence the Future is employed instead of the Potential.

Why do we use the phrase सिद्धाप्रयोगे 'when the actual result does not take place'? Observe, अलं देवदत्तो हस्तिनं हनिष्यति 'Devadatta is in a position to kill the elephant, and he will carry it out also'.

Under similar circumstances, in past and future times, when non-completion of action is indicated, the Conditional tense (लृङ्) must be invariably used in preference to every other tense. Professor Bohtlingk translates the sutra thus: "The Potential is employed when it is expressed that some one is believed to be capable of doing something, pre-supposing that the actual performance of the action does not take place".