I have trouble with the subjunctive mood and will try to reduce my confusion in this section. The first part is based on The Allen & Bacon Handbook, by L.J. Rosen and L. Behrens).
Verbs in English can be in the indicative, imperative, or subjunctive mood. We use the indicative mood when we state a fact, opinion, or question; most sentences will be in the indicative mood. We use the imperative mood for commands and the subjunctive mood when explicitly referring to an unreal or hypothetical situation or when expressing doubt. doubt or
When 'if clauses' describe an unreal or hypothetical situation, the subjunctive mood is used with would, could, might, or should in the main clause and were in the dependent clause.
If the variance were less, we could separate the means.
But if the dependent clauses introduces a possible cause-and-effect relationship (a relationship that is true or quite possible), use the indicative mood.
If the variance is small, we can separate the means.
Do not use would or could in subjunctive clauses starting with if, as if, or as though.
If we would have used more replicates, the variance would have been less.
If we had used more replicates, the variance would have been less.
Possible or real statements about the future
If we have enough plants, we will start the experiment next week (indicative mood)
Hypothetical or unreal statements about the future
If we had started enough plants, we would start the experiment next week (past subjunctive mood)
Expressing a wish or suggestion in the present for a hypothetical event
He wishes [that] we had more replicates.
He wishes [that] he were finished.
He wishes we could increase the replication
He wishes he could finish.
Garner (A Dictionary of Modern American Usage) states that 'the subjunctive mood of the verb appears primarily in six contexts' (I modeled the examples after those provided by Garner):
'conditions contrary to fact'
If I were (indicative = am) the principal investigator, the experiments would be completed by now.
If I were (indicative = was) to increase the replications, I would need to reduce the treatments.
I wish that I were (indicative = was) able to increase the replications.
I insisted that he increase (indicative = increases) the replications.
I suggest that she increase (indicative = increases) the replications.
'statements of necessity'
They must be thorough (indicative = are).