# Would have v3 for guess or assumption in the past

I have seen a usage of would have v3 which do not fit into the known area of conditional type 3 and is used for completely different purposes.

In a court of law, a judge is asking a woman and a man questions about the case, where the woman accuses the man of stealing her money 2 years ago. So the judge asks them a lot of questions, to understand the case properly, like: How did it happen? When did it happen?

The judge asks the woman, +How old was he at the time he stole the money?"

The woman takes time to think and answers a few seconds later, "Eerrr, hmm.... He would have been 17."

So, she used "would have v3" for a guess or a speculation in the past, not for an unreal situation. It is interesting that she did not give the answer "He was 17". I have never seen such a usage. she could have said "He must have been 17" to empasize a strong guess in the past.

Why do you think she said "He would have been 17" but not "He was 17"? Can we use would have v3 for such a speculation or a guess in the past?

If yes, how will it differ from "must have v3" which is also used for a guess or an assumption in the past.

• My only assumption so far is that: The boy who they are talking about was somewhere close to 17 years old but he died before he hit 17. So she's emphasizing this particular part that he was between 16 and 17 years. – SovereignSun Mar 16 '17 at 14:51
• Perfect Continuous Conditional can be used in type 3 conditional sentences. It refers to the unfulfilled result of the action in the if-clause, and expresses this result as an unfinished or continuous action. So logically: He would have been 17 years old (but he wasn't) when he stole the money. – SovereignSun Mar 16 '17 at 14:54
• "He must have been 17" makes us think that she wasn't sure of his age; it may have been less or more than 16, but "He would have been 17" clearly defines that is was less than 17. She could have said "He was 17" if she certainly new his exact age at that time. – SovereignSun Mar 16 '17 at 14:57
• @SovereignSun You would have been right, except the question states that the man in question is alive two years later in the courtroom ;) – relaxing Mar 16 '17 at 15:30
• The man is alive and in the court standing next to the woman. – yunus Mar 17 '17 at 11:27