164. The forms of the verb may be divided among three stems, called (1) the Present, (2) the Perfect, and (3) the Supine stem.
1. On the Present stem are formed:
The Present, Imperfect, and Future Indicative, Active and Passive.
The Present and Imperfect Subjunctive, Active and Passive.
The Imperative, Active and Passive.
The Present Infinitive, Active and Passive.
The Present Participle, the Gerundive, and the Gerund.
2. On the Perfect stem are formed:
The Perfect, Pluperfect, and Future Perfect Indicative Active.
The Perfect and Pluperfect Subjunctive Active.
The Perfect Infinitive Active.
3. On the Supine stem are formed:1
a. The Perfect Passive Participle, which combines with the forms of the verb sum (be) to make—
The Perfect, Pluperfect, and Future Perfect Indicative Passive.
The Perfect and Pluperfect Subjunctive Passive.
The Perfect Infinitive Passive.
b.The Future Active Participle, which combines with esse to make the Future Active Infinitive.
c. The Supine in -um and -ū. The Supine in -um combines with īrī to make the Future Passive Infinitive (§ 203.a).
-tūra, etc., see § 238.b, Note 1), were felt by the Romans as belonging to one system, and are conveniently associated with the Supine Stem. Thus, from pingō, we have pictum, pictus, pictūrus, pictor, pictūra; from rīdeō, rīsum (for † rīd-tum), rīsus (participle), rīsus (noun), rīsūrus, rīsiō, rīsor, rīsibilis.