Where a contingent promise (a reciprocal agreement) or apprehension is implied, the affix leṭ (Vedic Subjunctive) is used after a root in the chandas (Vedas) Literature.,
The word उपसम्वाद means 'reciprocal agreement, contracting to do'. Thus यदि मे भवानिदं कुर्य्याद् अहमपि भवत इदं दास्यामि 'If you do this for me, I will give this to you'. Agreements like these are called उपसम्वाद; while guessing or inferring the result from a cause is called आशङ्का 'apprehension or fear'.
Thus अहमेव पशूनामीशै ॥ मदग्रा एव वो ग्रहा गृह्यान्तै ॥ मद्देवत्यान्येव वः पात्राण्युच्यान्तै ॥ नेज्जिह्यायन्तो (or नेज्जिह्यायन्त्यो) नरकं पताम ॥ (Nir. I. II. Bohtlingk) = जिह्माचरणेन नरकपात आशङ्कयते ॥ All the above examples have the sense of Potential, but the Subjunctive (Let) must be employed necessarily in these senses and not optionally, which anuvritti was understood in the last sutra.,