I. How to form subjunctives:

          (A) For Present "use the wrong vowel":  -e,   -ea,  -a,  ia.

For present subjunctive, active and passive, Latin makes use of a basic alternation between -e- and -a-:  a-stem verbs use -e-; all others (which normally have e/i/u) use -a-.

Study the following examples in 3rd singular.

     (1st/2nd parts)               (subjunctive, active and passive)

voco, vocāre  —>            vocet           vocētur

deleo, delēre  —>             deleat          deleātur

duco, ducere  —>             ducat         ducātur

capio, capere —>           capiat          capiātur

audio, audīre  —>         audiat         audiātur

          (B)  Imperfect uses present infinitives + endings.

voco            —>             vocaret        vocarētur

deleo            —>             deleret         delerētur

duco            —>             duceret        ducerētur

capio           —>             caperet        caperētur

audio          —>             audiret        audirētur

          (C)  The Perfect and Pluperfect are more complicated

(1)  Perfect Active uses 3rd part (drop -i) + eri + endings

vocav(i)      —>  vocav-eri-t              delev(i) —>  delev-eri-t

dux(i)         —> dux-eri-t                  audiv(i)—> audiv-eri-t

(2)  Pluperfect Active uses perfect infinitive (=3rd part + sse) + endings

vocavi —> vocav-isse-t                     delevi —> delev-isse-t

duxi —> dux-isse-t                          audivi —> audiv-isse-t

(3) Perfect and Pluperfect Passive use the 4th part + subjunctive of sum, esse

perfect passive (may have been ...)   vocatus sit,                  deletus sit

ductus sit                                 captus sit                                 auditus sit

pluperfect passive (might have been...) uses 4th part + impf. subjunctive

vocatus esset                            deletus  esset

ductus esset                              auditus esset.