Conditional sentences - variations

Type 1

1. Statements of general truths, habitual behaviour, e.g.
If we boil water, it evaporates. can be written in the past form: e.g.
If we boiled water, it evaporated. (if = whenever) If I went abroad, I visited famous museums. (= it was my habit whenever I went abroad)

2. The introducion of should in the conditional clause makes the condition less likely, should = by any chance e.g.
If you should see him, tell him we would like to hear from him (= it is not very likely that you will see him)

3. The introduction of will (would) in the conditional clause indicates the speaker's appeal for co-operation, agreement or willingness of the subject, e.g.
If you will (would) wait a minute, I'll be ready in no time.

Type 2

1) The introduction of were to in the conditional clause makes the conditic suppositional,

2) The introduction of would in the conditional clause corresponds to the use of will/would in Type 1, i.e. it is the speaker's appeal for the co-operation of the subject. This use may refer to a real situation in which the speaker wishes his appeal sound more tentative,
e.g. If you would wait for me, I'd be most grateful.

3) Present unreality, i.e. something contrary to the present fact, is conveyed by the use of the past tense after such expressions as I wish, if only, as if, I'd rather, it's high time, suppose,
e.g. I wish you were punctual! (but you are not)
It's high time we started. (we haven't started yet)
Suppose we didn't know the way. (but we do know)
If the subject's wishes are frustrated, we can use would + infinitive instead of the past tense,
e.g. I wish you would be punctual (but you never are)

Type 3

1) The introduction of were to + perfect infinitive makes the condition even more hypothetical,
e.g. If I were to have known about your accident, I would have arrived earlier. (but I didn't have the slighest idea)

2) Past unreality, i.e. something contrary to the past fact, is conveyed by the use of the Past Perfect Tense after / wish etc.
(see: Present unreality — above), e.g. I wish you had been punctual! (but you were not) If only you had told me! (but you didn't)