Articles – Why ‘I Have the Brown Eyes’ Is Incorrect Compared to ‘I Have Brown Eyes’

As far as I know, the article the comes from the old English word for that (if something has a the in front of it, you can point at it). So, you can kind of mentally substitute the with that (or those for things that are plural) and if the whole thing still makes sense, then the usage is most likely correct. The indefinite article a/an, again, comes from the old English word for one. I usually think of it like this:

Volvo is a car. It is a car because it is just one of many possible cars that exist.

or

Volvo is a car. It is a car because it is one example of the nebulous idea of car.

Another example:

I'm gonna buy a car. I'm gonna buy just one out of many cars that exist.

With the, I think, we will typically be able to add some very specific information about the object we are talking about. For example:

I saw the man again. (The man that we met yesterday and his name was John.)

Where are the kids, honey? (The kids that are named Jimmy and Bobby because they are our sons.)

Compare that with examples using a:

I saw a man again. (maybe in my dream) (just a man, one of the class man)

What do kids like most of all, honey? (just kids in general, not our children or our future children)

The "zero article", otherwise known as simply not using an article, either indicates a proper name, or an abstract concept.

Apple is the most common fruit in the region.

This cannot be correct, because you are not talking about the abstract concept of an apple, but rather about a very real and concrete object.

Apple is the platonic ideal of fruit.

This example is closer to correct, because we are now talking about the concept of the apple, but even here, apple is simple to real and concrete to be usable with the zero article. This is also wrong.

Apple is on my mind.

Finally, we have come to a correct sentence, thoroughly converting a concrete noun into an abstract concept that I am merely thinking about. But even here, alone, without context, the idea of treating the word "apple" as an abstract concept is so strange that most people would reinterpret the sentence to treat "Apple" as a proper noun instead, especially since there exists a very real and well known company with the proper name of "Apple". But it does work, grammatically, the other way... it's just a very strange idea. You might find it in a philosophy textbook.