Which one is correct?
When I was a kid
or
when I was kid
Kid is a general idea there. So should it be without the identifier? And also
I sleep during a day
or
I sleep during day
Isn't day a general idea? So why should it be a day?
Which one is correct?
When I was a kid
or
when I was kid
Kid is a general idea there. So should it be without the identifier? And also
I sleep during a day
or
I sleep during day
Isn't day a general idea? So why should it be a day?
"Kid" here is actually not a "general idea", but rather a specific noun.
I was a kid.
I was one of many kids (in the world).
Many kids have existed, and I was one of them.
While these three sentences have different emphasis, the basic meaning of them is pretty similar.
I was kid.
Here, with the zero article, "kid" is no longer a specific thing, but now either a name or an abstract concept, such as a platonic form. If "kid" is supposed to be a name, you should capitalize the "k". If "kid" is supposed to be an abstract concept... well, that idea is simply a bizarre and non-sensical. A "kid" is a real thing, not a thought. In almost any context this is simply wrong.
I was a kid.
This is correct.
Now moving on...
I sleep during a day.
Day, again, is usually not an abstract idea. It is a very concrete thing; that is, it is the time between sunrise and sunset. Here, we are not talking about any day, but rather the difference between day and night. In the category of "day and night", there is only one day, so we don't use the indeterminate article "a", but instead the definite article "the".
I sleep during the day (and not the night).
This is correct.
Now in this case, it is less strange to treat "day" as an abstract concept, akin the platonic forms. In this sense, it is grammatically acceptable to say
I sleep during day.
That said, this construction is a little strange. I would understand it and accept it, but I almost certainly would not say it. It is easier to understand "day" as a concrete noun than an abstract noun.