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Dear teachers,
I don;t understand exactly the meaning of the sentence in bold below ,which I take from an on-line newspaper.Could you possibly explain it to me?:

Biogas has historically been used in internal combustion engines. However, the use has been limited to large-sized engines which use gas extracted from dumping grounds or sewage. Until now, small-sized engines using biogas were uncommon.

1/Does it mean that now small-sized engines are common or Does it mean that now small-sized engines using biogas are not common?

2/"Until now" refers to "a period up to now",then why is it that the present perfect is not used here?i.e. Until now, small-sized engines using biogas have been uncommon.

I am very confused. Please help me understand it.

Thank you in adcance
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Comments  
Tuongvan1/Does it mean that now small-sized engines are common or Does it mean that now small-sized engines using biogas are not common?
It means that small-sized engines which use biogas were uncommon before, but they are not uncommon now.
Tuongvan2/"Until now" refers to "a period up to now",then why is it that the present perfect is not used here?i.e. Until now, small-sized engines using biogas have been uncommon.
It may have been "a slip of the pen". Your version with have beenis better. Emotion: smile

CJ
Thank you Califjim,
What do you mean by saying""a slip of the pen"?
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Dear Califjim,
My friend tells me that in this context "Until now, small-sized engines using biogas have been uncommon" is different from "Until now, small-sized engines using biogas were uncommon"
"Until now, small-sized engines using biogas have been uncommon" means"now small-sized engines using biogas are still uncommon" while"Until now, small-sized engines using biogas were uncommon" means" they were uncommon before but now they not uncommon any more.

Please help explain it . I am confused about this problem
Tuongvan"a slip of the pen"?
It's a way of saying "mistake". The writer was writing with his pen, and his pen slipped out of his control, and wrote something incorrect!!! Emotion: big smile
CJ
TuongvanDear Califjim,
My friend tells me that in this context "Until now, small-sized engines using biogas have been uncommon" is different from "Until now, small-sized engines using biogas were uncommon"
"Until now, small-sized engines using biogas have been uncommon" means"now small-sized engines using biogas are still uncommon" while"Until now, small-sized engines using biogas were uncommon" means" they were uncommon before but now they not uncommon any more.

Please help explain it . I am confused about this problem

They both mean the same to me. To be very exact, they both mean that small-sized engines that use biogas were uncommon in the past, and have continued to be uncommon, and are still uncommon very near the time of writing the statement. And they both invite the reader to conclude, on the basis of context, that a change has occurred very recently, and that small-sized engines that use biogas are not so uncommon now as in the past, or to conclude, perhaps, that such a change will occur soon.

The difference is that the one with the present perfect (have been ...) is the correct way to say it.
___

You have to distinguish between what the statement actually says, and what it assumes the reader will conclude from it.
If I say that sugar has been cheap until now, I may be suggesting, without saying it, that I have noticed that the price of sugar has very recently increased or that I think it will soon increase. (I could say, somewhat incorrectly, that sugar was cheap until now, but it would mean the same thing.)
If I say that Sue's piano lessons have been easy until now, I may be suggesting, without saying it, that Sue's piano lessons have very recently become more difficult, or that I think they will soon become so. (I could say, somewhat incorrectly, that her piano lessons were easy until now, but it would mean the same thing.)
If I say that Charles hasn't had any problems with his car until now, I may be suggesting, without saying it, that Charles has very recently begun to have problems with his car, or that I think he will soon have problems with it. (I could say, somewhat incorrectly, that he didn't have any problems with his car until now, but it would mean the same thing.)
But notice that much of the meaning resides in what it suggests, not what it actually says. Because of this, we can deny the suggested implications, thus:
Sugar has been cheap until now. I certainly hope that it continues to be cheap.
Sue's piano lessons have been easy until now. Her teacher says the lessons will be just as easy in the future.
Charles hasn't had any problems with his car until now. If his luck continues, he may never have a problem with it.
But most of the time, we don't deny the suggested implications. We allow the reader to conclude that some change has occurred. The tendency to conclude that a change has occurred is especially strong when the sentence has a negative, for example the third sentence above (hasn't had any problems) and, to a lesser extent, your original example (with uncommon).
CJ
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Thank you Califjim, butcan I say like this?:

Situation1: I have just come back to my home town and I meet my close friend Jack again in my home town after a long separation of 3 years and I say to him:

Hi Jack! I missed you very much.I have wanted to meet you for a long time,but I was very busy.Until now, I couldn't meet you
When saying "Until now, I couldn't /was unable to meet you " I mean "in the past I couldn't visit him.Now I can visit him"

Situation 2:I have a friend . His name is Jack.I want to meet him but I can't because I don't know where he is now.
So I say to my mother:" I have been searching for Jack for a long time,but until now, I haven't met him .
When saying" until now, I haven't met him ." I mean" now I still haven't met Jack yet

Thank you in advance
TuongvanSituation1: I have just come back to my home town and I meet my close friend Jack again in my home town after a long separation of 3 years and I say to him:

Hi Jack! I missed you very much.I have wanted to meet you for a long time,but I was very busy.Until now, I couldn't meet you
When saying "Until now, I couldn't /was unable to meet you " I mean "in the past I couldn't visit him.Now I can visit him"
I would say
I've wanted to contact you for a long time, but I haven't been able to until now because I've been so busy.
TuongvanSituation 2:I have a friend . His name is Jack.I want to meet him but I can't because I don't know where he is now.
So I say to my mother:" I have been searching for Jack for a long time,but until now, I haven't met him .
When saying" until now, I haven't met him ." I mean" now I still haven't met Jack yet
I would say
I've been trying to get in contact with Jack for a long time, but I haven't succeeded [yet / so far].
I would not use until now because of the implications I mentioned in a previous post. That is, after the negative haven't, until now suggests strongly that a change has occurred, and now (or very recently) I have succeeded in contacting him. I would substitute yet or so far because they don't have the same implications.
CJ
Dear Califjim,
Sorry for having troubled you and Clive so much, but infact I am still confused about the use of UNTIL NOW/TODAY with various tenses.To make sure, how about this sentence, which I picked up from Collin Build Dictionary?:

Until now, safety needles have not been widely used because they cost more

Does it mean that now people haven't used them widely yet because theu are expensive ? or does it mean that now people have started to use these needles widely ?

Another sentence in my grammar book:

I have never been happy up until now

Does it mean that now I am still unhappy? or does it mean that In the past I was not happy but now I am happy?
As far as I know this sentence means that in the past I was not happy and now (at this time of speaking) I am still unhappy
Thank you in advance
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