Are these phrases correct?

[RussianT]

Dear teachers! I'm a teacher of English from Russia. Please help me and my colleagues to find the truth. My question is very easy and may be a little bit silly, but believe me it is very important to know the answer.
So, are phrases below correct (there is no context, each phrase is used out of context in exercises):

A rabbit is black.
A cat runs.

Thank you.

 

[birdeen's call]

I'm not a teacher and I'm not an expert, but here are my thoughts.

First of all, do you really mean phrases or do you mean sentences? I'm asking because you used capitalization and periods.

If you mean phrases, then they're correct in my opinion no matter what you mean by "correct".

If you mean sentences, then I think it depends on what you mean by "correct". If you mean syntactic correctness, then yes, they're correct. If you mean, "Is there any context in which this sentence could be used", then I'm not sure -- I don't see such contexts but it surely doesn't mean they don't exist.

 

[masuas]

I think that, for sure, a cat runs when it has to.
A rabbit, can be black, or white or brown, whatever colour.
But if you say "a rabbit is black", depends; it would be like saying " the moon is white",
because that is the colour of the moon. But rabbits come in different colours and sizes.
A rabbit " is black", is an emphatic affirmation.

Greetings from the Iron Babel

 

[RussianT]

Thank you very much for your answers!

The problem is one of my colleagues uses these phrases to teach little children how to use "is" and "-s". But my second colleague says that it’s wrong to use them, because these phrases don't exist; it's right to use only "THE rabbit is black" and "THE cat runs".

 

[bhaisahab]

Thank you very much for your answers!

The problem is one of my colleagues uses these phrases to teach little children how to use "is" and "-s". But my second colleague says that it’s wrong to use them, because these phrases don't exist; it's right to use only "THE rabbit is black" and "THE cat runs".

"The" is better.

 

[masuas]

Definitely makes a big difference with the article "the", as bhaisahab mentioned.
It makes it more descriptive as you said. The bird flies, the lion hunts, the children read
in class.
Hope I was able to help.
Masuás

 

[birdeen's call]

Thank you very much for your answers!

The problem is one of my colleagues uses these phrases to teach little children how to use "is" and "-s". But my second colleague says that it’s wrong to use them, because these phrases don't exist; it's right to use only "THE rabbit is black" and "THE cat runs".

You seem not to distinguish between phrases and sentences. A phrase is a sequence of words that makes sense. So, as in Gillnetter's examples, your phrases are good. But as stand-alone sentences, I'm not sure if they're of any use.