Here’s a common grammatical mistake I see: the use of the verb phrase “would have” after an “if” clause. For example, try this: “If Sigwald would have paid more attention to his martial arts training, then we wouldn’t have lost.”
The use of “would have” in a clause introduced by “if” is always, always wrong. Technically speaking, “would have” is a conditional perfect construction, and it just doesn’t belong after an if. Because “would have” expresses a conditional mood, it is used only for hypothetical situations – such as in clauses introduced by “then.”
For example, you would say, “If Sigwald had wanted to fight the invading army, then he would have joined the other men as they swarmed the town walls to pour hot tar on the enemy.”
In that sentence, I am expressing a hypothetical: Sigwald did not fight because he didn’t want to, but hypothetically, if he’d wanted to, then we’d have found him among the ranks.
Notice that in my example sentence, the “would have” applies not to what Sigwald actually did, but to what he might have done, had the situation been different. What he actually did was not want to fight. What he might have done was join the other townsfolk. That’s why I did not use “would have” in conjunction with the “if”: we know already that Sigwald didn’t want to fight. It isn’t conditional at all.
What was conditional in my sentence was the hypothetical outcome of a desire Sigwald clearly did not possess. And since it is hypothetical, I therefore did use the conditional “would have” with the “then” clause.
If this seems confusing, remember that when you are stating in an if clause what a character actually did or did not do – break the alien’s telepathic hold, create a monstrous chimera, or fail to make it to the wormhole in time to get back to the Alpha Quadrant – do not use “would have.” On the other hand, when you are stating the outcome that then did not happen, it is proper to use “would have.”