at a zero-to-eighteen-month level of a typical development (article use)

[Alexey86]

I'll let jutfrank deal with that. He has more patience and stamina than I.

I understand. I would also leave this thread if it became a place only testing my patience and stamina.

[Alexey86]

For me, "Water boils at a temperature of 100 degrees Celsius" is a shorter way of saying:

Water boils at a specific temperature. What temperature? 100 degrees Celsius.

I can apply this logic to the floor example: I'm on a certain floor. What floor? The fifth one. => I'm on the fifth floor.

So, why does a specific temperature lead us to a temperature of 100 degrees, while a certain floor doesn't lead us to a fifth floor?
Or, what am I missing?

[jutfrank]

So, why does a specific temperature lead us to a temperature of 100 degrees, while a certain floor doesn't lead us to a fifth floor?
Or, what am I missing?

I feel I'm failing dismally to explain this. I'll try one last approach, using your 'floor' analogy.

Let's leave naturalness aside completely for a moment and compare these two sentences:

He's on the fifth floor.
He's on a fifth floor.

What does the second sentence mean? Well, it can mean either of the following:

a) The building that he is in has more than one fifth floor, and he's on one of those fifth floors.
b) The building that he is in has only one fifth floor. This particular fifth floor is just one instantiation of many possible instantiations of fifth floors.

It seems to me that you are stuck in interpretation a), which obviously doesn't make a lot of sense. In fact, to go further, to you it makes no sense at all because in your 'floor' model, it is not possible for a building to have multiple fifth floors.

This should then lead you to adopt interpretation b), which is what I've been trying to suggest. Using the 'floor' analogy, we can imagine that the world consists of multiple buildings, all with fifth floors, and he's on one of them.

I really don't think I can put it any clearer than that.

[Alexey86]

b) The building that he is in has only one fifth floor. This particular fifth floor is just one instantiation of many possible instantiations of fifth floors.

Three questions:
1) If I asked you what floor the man on the picture below is on (NOT: which floor of the rightmost building), what would you say?
2) If you were to ask me to show you any third floor, how would you do that (without any): Show me a third floor (my choice) or Show me the third floor?
3) If you use different articles with floor in 1) and 2), why?

[jutfrank]

Three questions:
1) If I asked you what floor the man on the picture below is on (NOT: which floor of the rightmost building), what would you say?
2) If you were to ask me to show you any third floor, how would you do that (without any): Show me a third floor (my choice) or Show me the third floor?
3) If you use different articles with floor in 1) and 2), why?

Sorry, I don't follow. (Nice pictures, by the way.)

Did you understand my point about how something can be one and many at once?

[emsr2d2]

If you showed me that picture and said "Show me a third floor", I would point to one of the third floors that are visible. If you said "Show me the third floor", I would have to ask "Of which building?" If you asked me where the man was, I would be able to use the definite article - "He's at the left-hand window of the second floor of the building on the right".

[Alexey86]

Did you understand my point about how something can be one and many at once?

It would really help me to understand if you answered my questions above. What do you not follow exactly?

[Alexey86]

If you showed me that picture and said "Show me a third floor", I would point to one of third floors that are visible

That's clear, thank you.

If you asked me where the man was, I would be able to use the definite article - "He's at the left-hand window of the second floor of the building on the right".

But that's a different question! My question is What floor the man is on?

[emsr2d2]

But that's a different question! My question is What floor is the man is on?

And my answer would be "He's on the second floor". A man can only be in one place at one time. Your question does not need to elicit the information that we're talking about the building on the right because that's where we can see him. That building has only one second floor.

[jutfrank]

What do you not follow exactly?

What the point of the questions is.

My question is What floor the man is on?

I think the answer you want me to give here is: He's on a third floor. Is that what you mean?