There are actually some very clear-cut rules for which subjunctive form to use in sentences. It all depends on what tense is used in the main clause of the sentence.
Thnk about it. We can react to something in the past or in the present. We can tell someone to do something now or we could have told them yesterday. That opening part of the sentence, whether it's happening now/later or in the past will determine the subjunctive form we need to use. Some examples of main clauses or openers are:
We can react in the PRESENT...
Me sorprende que...
Es bueno que...
Dudo que...
Or we can react in the PAST...
Me sorprendió que...
Era bueno que...
Dudaba que...
There are 2 parts of the Sequence of Tenses in Spanish presented below. The first part addresses how to know when to use present or present perfect subjunctive vs imperfect or past perfect subjunctive in regular statements. The second part addresses the tenses used in "IF Clauses".
SEQUENCE OF TENSES for subjunctive statements
| Indicative tense in main clause | connector | Subjunctive tense in dependent clause |
|---|---|---|
| PRESENT | que | PRESENT SUBJUNCTIVE or PRESENT PERFECT SUBJUNCTIVE |
| FUTURE | que | PRESENT SUBJUNCTIVE or PRESENT PERFECT SUBJUNCTIVE |
| COMMAND | que | PRESENT SUBJUNCTIVE or PRESENT PERFECT SUBJUNCTIVE |
| PRETERIT | que | IMPERFECT SUBJUNCTIVE or PAST PERFECT SUBJUNCTIVE |
| IMPERFECT | que | IMPERFECT SUBJUNCTIVE or PAST PERFECT SUBJUNCTIVE |
| CONDITIONAL | que | IMPERFECT SUBJUNCTIVE or PAST PERFECT SUBJUNCTIVE |
Espero que él venga al cine con nosotros.
Será posible que él venga al cine con nosotros.
Me alegró que él viniera con nosotros.
Yo dudaba que él viniera al cine.
SEQUENCE OF TENSES for IF Clauses
| SI Clause (IF...) | Result clause (THEN...) |
|---|---|
| Si + PRESENT INDICATIVE | PRESENT INDICATIVE |
| Si + PRESENT INDICATIVE | FUTURE |
| Si + PRESENT INDICATIVE | IMPERATIVE |
| Si + IMPERFECT SUBJUNCTIVE | CONDITIONAL |
| Si + PAST PERFECT SUBJUNCTIVE | CONDITIONAL PERFECT |
*Notice you will never use present subjunctive in an IF statement.
Si yo tengo el tiempo, voy al cine este fin de semana.
Si yo tuviera el dinero, compraría una casa nueva.
Si yo hubiera venido más temprano, te habría saludado antes de la reunión.
The video below walks through using these two charts to determine the appropriate tense.