Adding "one" to the end of a sentence

Hi, can anyone tell me why I have to say "one" at the end of the following sentence:-

Which car is yours?
It's the blue one. Can't I just say "It's the blue."

but I don't have to say "one" at the end of this next answer:-

Which dog is yours?
It's the biggest.

Thanks!

NOT A TEACHER

Quote:

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Originally Posted by crazyaboutenglish

Hi, can anyone tell me why I have to say "one" at the end of the following sentence:-

Which car is yours?
It's the blue one. Can't I just say "It's the blue."

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“One” is used to mean someone or something of a type that has already been mentioned or is known about (see #1 here one - Definition from Longman English Dictionary Online for more examples).

Quote:

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Originally Posted by crazyaboutenglish

but I don't have to say "one" at the end of this next answer:-

Which dog is yours?
It's the biggest.

Thanks!

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I don’t know about that. Perhaps it's possible, I'm not quite sure. I’d still say, ‘It’s the biggest dog’, or ‘It’s the biggest one’.

Thank you!!!

NOT A TEACHER


Hello, crazyaboutenglish:

You have asked a great question.

I think that I have found the answers in Mr. Michael Swan's Practical English Usage (1985 edition, entry no. 391.4 on page 392).

a. It's the blue car. As you can see, "blue" is an adjective. Mr. Swan says that if there is an adjective, you must use the word "one."

i. His example: I would like that green one. (NOT: that green)

b. It's the biggest.

i. Mr. Swan says that one can be left out immediately after superlatives.

(a) Mr. Swan's example: I think that my dog's the fastest. / I think that my dog's the fastest one.


HAVE A NICE DAY!

No. Saying "it's the blue" would not sound correct.

"It's the biggest" sounds OK in that context.