Things get complicated when there are different time periods involved, as well as different degrees of certainty. They get complicated because in English we use the same verb tenses to describe both periods of time (time-frames) and degrees of certainty. As you can see in Figure 3, we have covered all of these possibilities and explained the contexts in which they can be used. This highlights the dual nature of the Past tenses.
Fig. 3 Certainty and Time-frame
Degree of Certainty | Time-frame of Condition | Time-frame of Result | |||
Certain outcome (Zero Conditional) | General truth | Present | If you freeze water, | Present | -it turns to ice. |
Likely outcome (First Conditional) | Prediction of what the speaker thinks will happen | Present/ Future | If you lend him money, (you probably will) If + present | Future | -he will return it. Will (verb) |
Past | If he heard your invitation yesterday and he knows he is invited, (You are assuming he heard) If + past | Future | -he will come today. Will (verb) | ||
Unfinished time (Perfect) | If you have met him before (you have probably met him) If + present perfect | Future | -you will recognize him again. Will (verb) | ||
Unlikely outcome | Prediction of what the speaker thinks will probably not happen | Present/ Future | If you lent him money, (you probably won’t) If + past | Present/Future | -he would return it. Would (verb) |
Impossible outcome | Description of what did not happen (condition) or cannot happen (result). Either the condition or the result or both are in a past time-frame. | Past | If you had lent him money, (you didn’t) If + past perfect | Past | -he would have returned it. Would have (verb) |
Future | If I were going to the awards ceremony tomorrow, If + past simple/continuous | Present | -I would be writing my acceptance speech now. Would be (verb) | ||
Future | If I were going to the awards ceremony tomorrow, If + past simple/continuous | Past | -I would have purchased a dress yesterday. Would have (verb) | ||