The third conditional is used when we are talking about the past and imagining something different from what actually happened:
| | Condition | Result | What actually happened |
|---|---|---|---|
| Past Perfect | WOULD HAVE + Past Participle | ||
| If | I had known, | I would have helped. | I didn't know and didn't help. |
| IF | Condition | Result | Certainty |
|---|---|---|---|
| past perfect | WOULD HAVE+ past participle | ||
| If | I had known, | I would have helped. | Although this didn't happen, the speaker is sure about the result. |
| If | I had known, | I could have helped. | Although this didn't happen, the result is only a possibility. |
| If | I had known, | I might have helped. | Although this didn't happen, the result is only a possibility. |
| If | you had known, | you should have helped. | Although this didn't happen, it is only a good suggestion or piece of advice. |
