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Difference between "must cost" and "must have cost"

Difference between "must cost" and "must have cost"

Difference between "must cost" and "must have cost"

(OP)
Hi there,

I've been trying 2 figure out the difference between "must have cost" and "must cost" in this example:

Jenny's engagement ring is enormous! It must have cost a fortune.

the sentence was taken from a modal verbs test: (http://www.englishpage.com/modals/interactivemodal8.htm). According to the solution, the correct answer is "must have cost".

I feel that this is the only right option, but cannot find any grammatical arguments for it.

Anybody? Please help.

RE: Difference between "must cost" and "must have cost"

"...must have cost a fortune." This is in the past. If Jenny is wearing it, it was certainly purchased in the past.

"...must cost a fortune." This is present tense, describing what its imagined cost is now.

Before, the cost was what the jeweler sold it for. Now, the cost is dependent on the bride-elect's level of happiness with her situation.  If her fiance is her true Prince Charming, she may consider it to be priceless. If she later finds him to be a philanderer, it may cost much less.

"must have cost" is speculative. If the cost were known, the observer might have said, "Jenny's engagement ring cost a fortune." Or she might have said, "Jenny's engagement ring did cost a fortune."

A  piece of advice for you, pyrszel. I advise against texting abbreviations in the forums.  "I've been trying 2 figure..." does not give the reader a good impression of the writer.

Good on ya,

Goober Dave

Haven't see the forum policies?  Do so now: Forum Policies
 

RE: Difference between "must cost" and "must have cost"

This is an example of the perfect infinitive.  The perfect infinitive is used to talk about things in the present with reference to an action which took place in the past.  Therein lies the difference between "must have cost" and "must cost".  Must have cost refers to the act of purchase which has already happened, i.e., the purchase was in the past.  Must cost implies the purchase has not yet happened.

Good Luck
--------------
As a circle of light increases so does the circumference of darkness around it. - Albert Einstein

RE: Difference between "must cost" and "must have cost"

(OP)
Alright... Thank You guys! :) I knew I just got stuck on it. This was really not that complicated after all, huh :P

RE: Difference between "must cost" and "must have cost"

looking at the question the answer is clearly (i hope i'm right !?) "it must have cost a fortune."

i don't know how you would use "must cost", even in present tense.  "it cost a fortune" is clearly acceptable (for Jenny or her betrothed to say/boast).

RE: Difference between "must cost" and "must have cost"

It must cost a fortune to maintain that lifestyle/run that vehicle/use that service/...

RE: Difference between "must cost" and "must have cost"

It really doesn't matter if you don't have a fortune to spend.  

That being said, if you spent the fortune, then you don't have it either... just the ring.

Mike McCann
MMC Engineering
http://mmcengineering.tripod.com
 

RE: Difference between "must cost" and "must have cost"

CajunCenturion,

Don't quite agree that "must cost" would always suggest that something has not yet happened, eg, it must cost a fortune to cruise on the QE2.  

It is a capital mistake to theorise before one has data. Insensibly one begins to twist facts to suit theories, instead of theories to suit facts. (Sherlock Holmes - A Scandal in Bohemia.)  

RE: Difference between "must cost" and "must have cost"

==> Don't quite agree that "must cost" would always suggest that something has not yet happened, eg, it must cost a fortune to cruise on the QE2.
I suspect that if one had already paid for the cruise, one would not say what it must cost, but rather what it did cost.  The person who is saying what it "must cost" is not likely to have already made the purchase.

Good Luck
--------------
As a circle of light increases so does the circumference of darkness around it. - Albert Einstein

RE: Difference between "must cost" and "must have cost"

"The person who is saying what it "must cost" is not likely to have already made the purchase."

That's if they intend to purchase a ticket - maybe just passing comment, therefore "it must cost a fortune to cruise on the QE2." is a statement without any real time reference.

It is a capital mistake to theorise before one has data. Insensibly one begins to twist facts to suit theories, instead of theories to suit facts. (Sherlock Holmes - A Scandal in Bohemia.)  

RE: Difference between "must cost" and "must have cost"

==> That's if they intend to purchase a ticket -
I don't think intent is any way a factor; either a purchase has taken place or a purchase that has not happened.

"Must have cost" refers to a purchase in the past tense, i.e., a purchase that has already taken place, and the speaker is speculating as to its cost.  "Must cost" is a present tense phrase referring to a purchase that has not taken place with the speaker speculating about the cost.

Good Luck
--------------
As a circle of light increases so does the circumference of darkness around it. - Albert Einstein

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