The affix tasi comes after that Ablative -5th case which has the force of an apādāna kāraka when this apādāna relation arises owing to the union with the verbs hīya (passive of hā) and ruha,
Thus ग्रामतः आगच्छति or ग्रामात्, so also चोरतः or चोरतो बिभेति, अध्ययनतः or अध्ययनात् पराजयते ॥ See Sutras (l. 4. 24), 1.4.25, and 1.4.26 &c. Not so when the verbs हीय and रुह govern the ablative : as, सार्थात् हीयते, पर्वताद् अवरोहति ॥ The form हीय is given in the sutra to indicate that the verb हा whose present tense is जहाति is to be taken, and not जिहीति ॥ Thus we have भूमितः उज्जिहीते or भूमेरुज्जिहीते ॥ How do you explain the use of \tasi\ in the following well-known verse: \मन्त्रो हीनः स्वरतो वर्णतो वा\? The words here are not in the ablative, but in the Instrumental case i. e. स्वरेण वर्णेन वा हीनः ॥,