[*] 159. The Gerund and Supine are used as follows:— [*] a. The Gerund is a verbal noun, corresponding in meaning to the English verbal noun in -ing (§ 502): as, loquendī causā, for the sake of speaking.
[*] Note.--The Gerund is found only in the oblique cases. A corresponding nominative is supplied by the Infinitive: thus, scrībere est ūtile, writing (to write) is useful; but, ars scrībendī, the art of writing.
[*] b. The Supine is in form a noun of the fourth declension (§ 94. b), found only in the accusative ending in -tum, -sum, and the dative or ablative ending in -tū, -sū. The Supine in -um is used after verbs and the Supine in -ū after adjectives (§§ 509, 510):—