प्रयोग एव प्रमाणशिरोमणिः,
अतश्च तदनुसारि व्याकरणम् ।
prayoga eva pramāṇa-śiromaṇiḥ,
ataś ca tad-anusāri vyākaraṇam |
(Amṛta-tīkā on Hari-nāmāmṛta-vyākaraṇa: 1244)
“Usage is the crest jewel of pramāṇas [in grammar], and thus vyākaraṇa [i.e., grammatical correctness] follows that [i.e., is determined to reflect established usage].”