|Zero||When or 'If' + present verb ,
present verb (Without WILL) .
Note: When rather than if can give a greater feeling of certainty.
|First||If + present verb , will + present verb.
Note: There are other possible modals besides will and other words apart from If. For example: Unless
|Second||If ... + past simple, .... + would (will in the past) + bare infinitive ..|
|Third||If ... had been (past perfect) ..., .... would have been (will in the past + present perfect) ....|
Although the mixed conditional form past perfect, + would + bare infinitive shown here is the most common. There are many other possible mixed conditionals. If a sentence makes clear sense, in terms of the tense meaning and it is different to all the standard conditional forms, then it may stand as a correct sentence.