Teachers regularly ask me grammar questions. They are often quite interesting and though I (almost always) know the answers, occasionally I can't easily explain. And some give me a little pause for thought.
Like the one today.
The teacher showed me four sentences in turn and asked me what the differences were.
Sentence one was this: A bicycle has two wheels.
That was nice and easy. I didn't explain it inexactly these terms but the gist of it was that it is saying that any member of the class “bicycle” will have two wheels.

Sentence two was this: The bicycle has two wheels.
My immediate interpretation was the obvious one.
This particular member of the class “bicycle” has two wheels.

Sentence number three was: A horse has four legs.
Just like sentence one my immediate interpretation was that it means that any member of class “horse” has four legs.

And, of course, sentence four, predictably, was this: The horse has four legs.
Unlike the “bicycle” example my interpretation here was that “horse” is a member of class “animal” and that all horses have four legs.

He nodded. My assessment was in line with what he'd read.
What he wanted to know was
a) can sentence two carry a similar interpretation to sentence four and vice-versa (The answer is of course, yes)
and b) why did I pick the different interpretations rather than the same one.

And that's where I couldn't answer. I could only say that they seemed like the correct interpretations to me even though the other one remained a possibility in each case.

As with many of these types of question, context usually solves any dilemmas. For me, I originally read sentence two as a statement of a class of vehicles, the bicycle rather than any particular bike in question (or under conversation).

Then there are sentences without articled subjects: e.g., "Man is a featherless biped."