An article that denotes class of objects

[AlexAD]

Hi, there.
I'm confused with some rules about articles where one of the rules says "we use a/an article to denote a class of objects, for example: When I write, I always use a pen" and the another one says "we use the to talk about a type of animal, machine, etc. an there they give us an example:
The giraffe is the tallest of all animals.
As to my point of view both of the examples denote a class of objects, isn't it?
Let me see you an another example:

You enter the house by the street door.

Can I just say
You enter a house by the street door?

Thanks in advance.

[AlexAD]

I've figured out that A giraffe is the tallest of all animals is correct
along with the The giraffe is the tallest of all animals.
So,You enter a house by the street door would be grammatically correct as well because a collection of objects is being meant by that. Though that sentence sounds very uncommon (at least for me).

[5jj]

Try some of the threads listed under 'Similar Threads' at the bottom of this page, then come back if you have any more questions.

[AlexAD]

I've read use of definite article for describing a class? topic few times but I'm not sure I've got this right. In the example I wrote we are speaking about houses like a class that encloses all houses and therefore I still reckon that
You enter a house by the street door is also correct unless I am missing some details...

[5jj]

I still reckon that
You enter a house by the street door is also correct unless I am missing some details...

It is correct.

You enter the house by the street door is incorrect, if you are talking about the class of houses.

[AlexAD]

Ok, but The giraffe is the tallest of all animals. is very similar to that one you mentioned above because there's also a connection with a class of animals called giraffe. This one is correct, isn't?

[Tdol]

[/I]So,You enter a house by the street door would be grammatically correct as well because a collection of objects is being meant by that. Though that sentence sounds very uncommon (at least for me).

It sounds uncommon, but it's correct. People might use the plural there as well, which might sound more natural as we don't tend to talk about houses in that way.

[AlexAD]

Well, let's focus on the following sentence:
The giraffe is the tallest of all animals?

I've got that example from Murphy's book and it seems very unacustomed that they were a mistake there. The giraffe is a class (actually it is a subclass) of animals and attention is paid to that fact in the sentence.

Ok, what can we say then considering another sentence compared with previous one?

You enter the house by the street door.

Why wouldn't we say that we're speaking about a house like a class of buildings?

P.S. I didn't make those examples up I'm just trying to find out what kind of book I'm learning says lie.

[5jj]

Part of the problem may lie in the form of the sentence. The following can all work when we are speaking about a class of nouns:

A noun is ...
The noun is ...
Nouns are ...

So, we could say, "The house as such did not exist before the xxth century BCE.

It is theoretically possible to say "You enter the house by the street door", but it is highly unlikely as the first mention of the class of houses.

[Khosro]

You can also take a look at this thread. In addition to other's useful replys, 'billmcd' mentions a rule which is in my opinion more accurate than what you have already found, because it points to "example" when it's about "a". Generally speaking I don't think that strict rules can help us with articles.

http://www.usingenglish.com/forum/as...e-bicycle.html