Explain 3rd conditional complex sentence

Question

Could you explain to me the bolded part of the sentence? Why do we use this tense/form? Is it correct?

If he had known that it would have upset you, he would have been more careful.

I understand that it is 3rd conditional and simple sentences are clear to me. But this bolded part confuses me.

Could we write: it would upset you or it had upset you? And why?

Where can I read a rule about dependent clauses in conditional sentences?

Answer 1

Semantically, there's little difference here between

If he had known it would upset you

and

If he had known it would have upset you.

When forming past unreal conditionals, it's common to use "would have". For example:

If I had known you were a vegetarian, I would have made a salad.

Although the hypothetical simple past ("would upset") is fine, your example sentence mimics this structure. Sometimes people speak or write without carefully thinking through the grammar.

That being said:

If he had known it had upset you ...

represents a different situation. In the first case, "would have upset you" suggests that he was immediately aware that you were upset, but "had upset you" instead suggests that he was not immediately aware that you were upset. To diagram it:

"it would have upset you"

1. He did something.
2. You became upset, and he noticed.
3. He felt bad about it.

"it had upset you"

1. He did something
2. You became upset
3. He later found out you became upset (by what he had done), and felt bad about it.

Unreal conditionals and perfect tenses each are used to describe a fairly specific set of circumstances. When you combine the two, the circumstances they describe become even more specific. It's not surprising that this phrasing seems confusing, because it's not often used.

Answer 2

I would favor the form without "have", specifically:

If he had known that it would upset you, he would have been more careful.

This is because, althoguh this is a hypothetical or subjunctive statement, we should be careful to keep track of the real and unreal parts, and the point-of-view in time.

that "It upset you" is real. That did happen. what is unreal is the "he knew" and the consequent that would have followed is his being more careful, and acting differently.

The (real) events that occured are:

1. He did something
2. That something upset you

(It may be that he felt bad afterwards, but the sentence doesn't say or imply that. He may not even know (yet) about the upset.)

The Hypothetical events are

1. He realizes that a certain action would upset you
2. Therefore, he is careful, and acts differently.

The point of view of the sentence is looking back to the moment before his action, where he could have realized (but did not) that it would cause you to be upset. Thus the event of the upset occurring is in the future of that moment. Therefore, I think that "would upset you" is better than "would have upset you", as "would have" is generally used when the speaker is looking back at an event which did not happen, not looking forward from such an event.

If he had known that it would have upset you, ...

suggests to me that the upset had already occurred, and that his hypothetical action would be not to prevent or avoid the upset, by acting differently and not causing it, but rather to deal differently with "you" to allow for the upset which had already occurred. Without additional context this is a slightly unlikely meaning, and so an unlikely form of words to use.