What are the uses of the subjunctive in main clauses?

There are four uses of the subjunctive in main clauses, the jussive, exhortative, deliberative and the conditional subjunctive. The jussive is the most common reason for a main clause subjunctive and can be easily translated with the english 'let'. eg. Romam eamus = Let us go to Rome. 

The exhortative subjunctive can be called the subjunctive of 'wish'. It is normally found with the introductory word 'utinam', making it easy to spot, although it can be found without. It is best translated with 'if only!' eg. Utinam dives sim! = If only I were rich!

A deliberative subjunctive can be easily spotted because it will be within a question. As such, the question mark at the end is a useful signpost. It is less certain than a normal direct question and so should be rendered into a more pensive style in English. eg. quid faciamus? = what are we to do?

The conditional main clause subjunctive occurs in the apodosis (second half) of a condition introduced by 'si' (if) eg. si fecissem, erravissem = If I had done this, I would have made a mistake. The italics are the apodosis.