Conditional sentences. “If” clause: verb in past tense, main clause: verb in present tense
Conditional sentences that contain an “if” clause in the past and end with the main clause in the present are generally expressing imaginative or hypothetical conditions. In these conditional sentences, the past perfect is used to refer to a past event. As a refresher, the past perfect expresses the idea that something occurred before in another action. These sentences can also show the reader that something happened before a specific time in the past. Therefore, the form of the unreal conditional sentence in this situation is as follows:
If + past perfect, would + have + past participle
Consider the following sentence
If I had had time, I would have cleaned the house.
The speaker in this sentence is informing their audience that they did not have time to clean the house.