edited by Meagan Ayer et al.
The Perfect System
169. The tenses of the Perfect System in the active voice are made from the Perfect stem as follows.
a. In the Perfect Indicative the endings -ī, -istī, etc. are added directly to the Perfect stem.
b. In the Pluperfect Indicative the suffix -eram, -erās, etc. is added to the Perfect stem.
Note— This seems to represent an older †-is-ām, etc. formed on the analogy of the Future Perfect in -erō (older †-is-ō, see c below) and influenced by eram (imperfect of sum) in comparison with erō (future of sum).
c. In the Future Perfect the suffix -erō, -eris, etc. is added to the Perfect stem.
Note— This formation was originally a subjunctive of the -s- Aorist, ending probably in †-is-ō. The -is- is doubtless the same as that seen in the 2nd person singular of the Perfect Indicative (vīd-is-tī), in the Perfect Infinitive (vīd-is-se), and in the Pluperfect Subjunctive (vīd-is-sem), s being the aorist sign and i probably an old stem vowel.
d. In the Perfect Subjunctive the suffix -erim, -eris, etc. is added to the Perfect stem.
Note— This formation was originally an Optative of the -s- Aorist (-er- for older
-is-, as in the Future Perfect, see c above). The i after r is the Optative mood-sign ī shortened (see § 168.e, Note 2). Forms in -īs, -īt, -īmus, -ītis, are sometimes found. The shortening in -ĭs, -ĭmus, -ĭtis, is due to confusion with the Future Perfect.
e. In the Pluperfect Subjunctive the suffix -issem, -issēs, etc. is added to the Perfect stem.
Note— Apparently this tense was formed on the analogy of the Pluperfect Indicative in †-is-ām (later -er-am, see b.), and influenced by essem (earlier †essēm) in its relation to eram (earlier †esām).1