a. In the Present Indicative the personal endings are added directly to the Present stem.
present stem arā- :
arā-s
arā-mus
arā-tis
b. In the Imperfect Indicative the suffix -bam , -bās , etc. (originally a complete verb) is added to the Present stem.
arā-bam
arā-bās
arā-bāmus 2
c. In the Future Indicative of the 1st and 2nd Conjugations a similar suffix, -bō , -bis , etc., is added to the Present stem.
arā-bō , arā-bis
monē-bō 3
d. In the Future Indicative of the 3rd and 4th Conjugations the terminations -am , -ēs , etc., are really Subjunctive endings used in a future sense (see e). The vowel was originally long throughout. For shortening, see § 167.
teg-am , teg-ēs
audi-am , audi-ēs
e. In the Present Subjunctive the personal endings were added to a form of the present stem ending in -ē- or -ā- , which was shortened in certain forms (§ 167).
ame-m , amē-s
tegā-mus , tega-nt
Note 1— The vowel ē (seen in the 1st Conjugation am-ë-s , etc.) is an inherited subjunctive mood sign. It appears to be the thematic vowel e (§ 174.1) lengthened. The ā of the other conjugations ( mone-ā-s , reg-ā-s , audi-ā-s ) is of uncertain origin.
Note 2— In a few irregular verbs a Present Subjunctive in -im , -īs , etc. occurs.
sim , sīs , sīmus ,
velim , velīs , etc.
This is an old optative, ī being a form of the Indo-European optative mood sign yē- (cf. siem , siēs , siet , § 170.b, Note). The vowel has been shortened in the first and third persons singular and the third person plural.
f. In the Imperfect Subjunctive the suffix -rem , -rēs , etc. is added to the Present stem.
amā-rem , amā-rēs
monē-rem
tege-rem
audī-rem 4
1.The conjugation of a verb consists of separate formations from a root, gradually grouped together, systematized, and supplemented by new formations made on old lines to supply deficiencies. Some of the forms were inherited from the parent speech; others were developed in the course of the history of the Italic dialects or of the Latin language itself.
2. The form † bam was apparently an Aorist of the Indo-European root BHU (cf. fuī , futūrus , φύω , English be , been ) and meant I was . This was added to a complete word, originally a case of a verbal noun, as in I was a-seeing ; hence vidē-bam . The form probably began in the 2nd or 3rd Conjugation and was extended to the others. The a was at first long, but was shortened in certain forms (§ 167).
3. The form † bō was probably a present tense of the root BHU , with a future meaning, and was affixed to a noun-form as described in footnote 2.
4. The stem element -rē - is of uncertain origin and is not found outside of Italic. The r is doubtless the Aorist sign s (cf. es-se-m , es-sē-s ) changed to r between two vowels (§ 15.4). The ē is probably the subjunctive mood-sign (see e., above).