I. Simple fact conditions (Here Latin uses the same moods
and tenses as English).
A. In present time: present indicative in both clauses.
Si laboras, vincis. If you work, you win.
B. In past time: imperfect or perfect indicative in both clauses.
Si laborabas (laboravisti), vincebas (vicisti). If you worked, you
II. Future conditions
A. Future more vivid (I am pretty sure that the action in the "if" clause
will occur): future or future perfect indicative in the "if" clause, future
indicative in the other clause.
Si laborabis (laboraveris), vinces. If you work you will win.
B. Future less vivid (I have some doubt that the action in the "if" clause
will occur): present subjunctive in both clauses.
Si labores, vincas. If you were to work, you would win. or If you
should work, you would win.
III. Contrary to fact conditions
A. In present time (the action in the "if" clause is not occurring):
imperfect subjunctive in both clauses.
Si laborares, vinceres. If you worked, you would win.
B. In past time (the action in the "if" clause did not occur: pluperfect
subjunctive in both clauses.
Si laboravisses, vicisses. If you had worked, you would have won.
Sample ExCET-type questions:
1. Fill in the blank in the following sentence:
Si Caesar Romam ______________, Cicero orationem faciat.
Answer: a, because the future less vivid condition requires the present subjunctive veniat.
2. Si Calpurniae credidisset, Caesar ad forum non isset.
The action in the first (conditional) clause of the above sentence:
a. might occur
b. did not occur
c. did occur
d. will occur
Answer: b, because the contrary to fact condition states that an action did not occur.