He must have lived here for five years.

[diamondcutter]

A: How long has Tom lived here by now?
B: He must have lived here for five years.
C: I’m not so sure. He may have lived here for four years or so.

(By me)
I’d like to know if the tense in the two sentences in red are correct in this context.

 

[Tarheel]

Say:

How long has Tom lived here?

Forget "by now". Forget it.

The answer would typically be "Five years" and not a full sentence.

Also possible:

A: How long has Tom lived here?
B. I'm not sure.

You don't want to use "so" there.

 

[diamondcutter]

Thanks, Tarheel.

I still want to know if the two sentences are grammatically correct in that context.

 

[5jj]

B: He must have lived here for five years.
C: I’m not so sure. He may have lived here for four years or so.

They are grammatically correct, though, as Tarheel suggested, not particularly natural.

If you really want complete sentences, this is more natural:

B: He must have lived here for five years.
C: I’m not so sure. It think it's more like four.

 

[Yankee]

Yes, but in B. it could suggest that the speaker knows or remembers something about Tom that could confirm the five years.

 

[Phaedrus]

A: How long has Tom lived here by now?
B: He must have lived here for five years.
C: I’m not so sure. He may have lived here for four years or so.

(By me)
I’d like to know if the tense in the two sentences in red are correct in this context.

I have been trying to hear "He must have lived here for five years" as referring to a five-year period that extends up to now, or to the time of speech, and have been unable to do so. To me, that sentence refers to a five-year period of time during which he lived here in the past. He ceased to live here before the time of speech. For full-sentence answers that accord with your intended meaning, I'd revise the dialogue like this:

A: How long has Tom lived here?
B: He has surely lived here for five years (by now).
C: I'm not so sure. It may only be for four years or so (that he has lived here).

 

[5jj]

I have been trying to hear "He must have lived here for five years" as referring to a five-year period that extends up to now, or to the time of speech, and have been unable to do so. To me, that sentence refers to a five-year period of time during which he lived here in the past.

That depends on context. If the question is 'How long has Tom lived here?', the assumption is that the time period extends up to the moment of speaking.
If the question is 'How long did Tom live here?', the assumption is that the time period ended in the past.

The answer in both situations is 'He must have lived here for five years'.

 

[Phaedrus]

That depends on context. If the question is 'How long has Tom lived here?', the assumption is that the time period extends up to the moment of speaking.
If the question is 'How long did Tom live here?', the assumption is that the time period ended in the past.

The answer in both situations is 'He must have lived here for five years'.

While I would understand the intended meaning if someone used the sentence "He must have lived here for five years" in answer to "How long has Tom lived here?," I can't imagine anyone felicitously using the sentence in response to that question, since "must have V-ed" seems (to me) inherently to refer to something that occurred or existed before the time of speech. Similarly, I wouldn't say, "I must have been a member here for at least five years," because I am still a member here.

 

[Tarheel]

Diamondcutter, when I invent a dialogue I have a context in mind. Also, if I can't think of a reason somebody might say a certain thing then I will not use that sentence.

:-|

 

[Tarheel]

Bob: He must have lived here for five years.
Clyde: What do you mean by that?
Bob: Well, I've known him for five years, and he's lived here all that time.
Clyde: Whatever.