When we talk about mixed conditionals, we are referring to conditional sentences that combine two different types of conditional patterns. The most common combination is the Type 3 conditional in the //-clause (if + past perfect) followed by the Type 2 conditional (would + infinitive) in the main clause. With this combination we are contrasting an imagined or real event in the past with the present result of that.
If the Maya had predicted weather changes better, their civilisation would probably survive today.
If Guttenberg hadn’t invented printing with movable type, people wouldn’t be able to publish so many books now.
We can also convey the same idea of past event and present result by using the Type 3 conditional (if + past perfect, would’ve + past participle) in both clauses. We use this type of conditional when we regret past action or inaction. If the Maya had predicted weather changes better, their civilisation would probably have survived.
If Guttenberg hadn’t invented printing with movable type, people wouldn’t have been able to publish so many books by now.