a. In the Perfect Indicative the endings -í, -istí, etc. are added directly to the perfect stem: as, amáv-istí, téx-istis.
b. In the Pluperfect Indicative the suffix -eram, -erás, etc. is added to the perfect stem: as, amáv-eram, monu-erás, téx-erat.
NOTE: This seems to represent an older -is-ám etc. formed on the analogy of the Future Perfect in -eró (older -is-ó: see c below) and influenced by eram (imperfect of sum) in comparison with eró (future of sum).
c. In the Future Perfect the suffix -eró, -eris, etc. is added to the perfect stem: as, amáv-eró, monu-eris, téx-erit.
NOTE: This formation was originally a subjunctive of the s-aorist, ending probably in -is-ó. The -is- is doubtless the same as that seen in the second person singular of the perfect indicative (víd-is-tí), in the perfect infinitive (víd-is-se), and in the pluperfect subjunctive (víd-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: as, amáv-erim, monu-eris, téx-erit.
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 í shortened (see § 168. e. N.2). Forms in -ís, -ít, -ímus, -ítis, are sometimes found. The shortening in -is, -imus, -itis, is due to confusion with the future perfect.
e. In the Pluperfect Subjunctive the suffix -issem, -issés, etc. is added to the perfect stem: as, amáv-issem, monu-issés, téx-isset.
NOTE: Apparently this tense was formed on the analogy of the pluperfect indicative in -is-ám (later -er-am, see b), and influenced by essem (earlier essém) in its relation to eram (earlier esám).[1][The signs of mood and tense are often said to be inserted between the root (or verb-stem) and the personal ending. No such insertion is possible in a language developed like the Latin. All true verb-forms are the result, as shown above, of composition; that is, of adding to the root or the stem either personal endings or fully developed auxiliaries (themselves containing the personal terminations), or of imitation of such processes. Thus vidébámus is made by adding to vidé-, originally a significant word or a form conceived as such, a full verbal form bámus, not by inserting -bá- between vidé- and -mus (§ 168, b).]