imoerfect subjunctive, when do i use ra instead of re?

Question

for example tuviere or tuviera? or estuviere estuviera, supiera supiera? when do you use one over the other

Answer 1

These days you use only the imperfect subj. Ends in -ra or -se.

Answer 2

Each one of the verbs that you have listed only has one imperfect subjunctive form. The other form is not imperfect subjunctive but future subjunctive, if I recall. Future subjunctive form is very rare so don't worry about learning it.

For the verbs you have listed, the imperfect subjunctive forms are:
tuviera
estuviera
supiera

Answer 3

One is past and the other is future

Imperfect (subjunctive) PAST tense:
tuvie-se, tuvie-ra
estuvie-se, estuvie-ra
supie-se, supie-ra

FUTURE (subjunctive):
tuvie-re
estuvie-re
etc.