Do we need the article 'The' here?
In general, for example:
- Sometimes, there aren't any clouds in the sky.
- Sometimes, there aren't any clouds in sky.

This is the confusion: I know that we don't use 'The' when we want to say something in general. And we use 'The' when we want to refer to a specific thing. So, according to this rule, I think the second sentence is correct, as I want to say that in general. However, I have doubts about it. Maybe I have learnt the rule wrongly. So, which one is correct?

Thank you in advance.

Question

Do we need the article 'The' here?
In general, for example:
- Sometimes, there aren't any clouds in the sky.
- Sometimes, there aren't any clouds in sky.

This is the confusion: I know that we don't use 'The' when we want to say something in general. And we use 'The' when we want to refer to a specific thing. So, according to this rule, I think the second sentence is correct, as I want to say that in general. However, I have doubts about it. Maybe I have learnt the rule wrongly. So, which one is correct?

Thank you in advance.

Answer

The first is correct. 
You are referring to something specific: the sky above you

Answer

Just like Peter said you're referring to something specific. You could say "The sky doesn't have clouds." and clouds wouldn't need a THE in front of it. Or if you were referring to a day without clouds you could say "Nothing but blue skies today." without a THE.