Why present perfect?

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Guest

#94799 Sat, 30 Apr 05 12:59 PM

The task is to complete the second sentence so that it has a similar meaning to the first
sentence, using the word given.

The thief ran right past you so I'm sure you saw his face.

must

The thief ran right past you so ....................................... his face.

My answer:
The thief ran right past you so must saw his face.

Correct answer:
The thief ran right past you so must have seen his face.

I admit that it sounds better with present perfect but the original sentence is in the past.

Guest

Present perfect

CalifJim

#94854 Sat, 30 Apr 05 06:01 PM

Rule: Modal verbs (and "must" is one of them) cannot be followed by a past tense form. To express past tense after a modal add "have" and the past participle. This is not truly a "present perfect" but a "modal perfect". In the case of the modal perfect construction the difference between simple past and present perfect is neutralized.

That is, adding "must" either to a simple past or to a present perfect creates the same modal perfect structure:

He read the book yesterday. > He must have read the book yesterday.
He has read the book twice. > He must have read the book twice.

CJ

CalifJim

Joined on Mon, Aug 2 2004

California

Veteran Member (17,568)

"There are no facts, only interpretations" - Nietzsche

Constructions, Difference between, Modal verbs, Modals, Past tenses, Present perfect, Simple past, Tenses, Verbs

temico

#94855 Sat, 30 Apr 05 06:12 PM

Quote:
"We use the Present Perfect to say that an action happened at an unspecified time BEFORE NOW. The exact time is not important."
----------"before now" = "past" ( to me, anyway)

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temico

Joined on Thu, Apr 21 2005

Full Member (274)

Present perfect

pieanne

#94858 Sat, 30 Apr 05 06:23 PM

Yes, but "unspecified time before now" is a kind of "chewing gum" period extending from say your birth day until today. Since you cannot pinpoint the EXACT moment in te past when the action took place, you can't use a simple past. THAT's when you use the present perfect.

pieanne

Joined on Thu, Jan 20 2005

South of France ...But I'm Belgian!

Veteran Member (7,512)

I'm glad to help, but I'm not a native! And please excuse my typos...

Present perfect, Simple past

paco2004

#94981 Sun, 01 May 05 04:15 AM

Rule: Modal verbs (and "must" is one of them) cannot be followed by a past tense form. To express past tense after a modal add "have" and the past participle. This is not truly a "present perfect" but a "modal perfect". In the case of the modal perfect construction the difference between simple past and present perfect is neutralized.

This rule seems rather simple but important. I have to keep it in mind.

He must have lived here for five years. / He has lived here for five years.

I must have met him five years ago. / I met him five years ago.

paco

paco2004