4

1)

a) A roof of a car is made of many different materials
b) The roof of a car is made of many different materials

2)

a) The branch of a tree will make decent firewood
b) A branch of a tree will make decent firewood

If we're talking about ageneral reference, not a spefic one, what's the correct ones ? a or b or both? if so what's the difference? What comes into play? Any extra comments would be appreciated.

4

In US English, there is no effective difference. The sentences that use the definite article are still not talking about a truly specific item since the indefinite article preceding the source negates any particularity.

In US usage the ... a ... is probably more frequent than a ... a ..., perhaps to help the listener focus on the part being described, or perhaps simply to avoid repetition.

SUPPLEMENT

Note that the examples given all talk about hypotheticals. They do not refer to a particular branch, tree, roof or car. While the ... a ... seems to be more definite than a ... a ..., the second indefinite article keeps the discussion hypothetical.

If the construction were changed to have only one article, it would have to be indefinite to preserve the hypothetical form.

A car roof is made of many different materials

and

A tree branch will make decent firewood

but not

The car roof is made of many different materials

or

The tree branch will make decent firewood

The latter two describe a particular roof and branch, not the theoretical roof or branch.

There are times that general reference descriptions use the definite article to describe a single item. In texts or narrations a singular example may stand in for the whole class.

The oak tree is a member of the deciduous group of trees.

This is a rather academic style, and in common speech would seem a bit pedantic.

3
  • does the fact that a tree has got many branches and a car has got just one roof changes the way you understand the meaning? – Dunno Oct 25 '13 at 7:44
  • 1
    No. The examples both concern themselves with singular items, a single branch or roof, whether the source has one or may of these items. – bib Oct 25 '13 at 12:11
  • 1
    What necessitates that The car roof is made of many different materials and The tree branch will make decent firewood pertain to particular rather than generic items? – pazzo Oct 12 '14 at 7:15
2

These are not normal articles.

They are used to mark Generic Noun Phrases of two different types,
which are named after the articles that distinguish them.

  • The roof of a car is a Definite Generic, which refers to the Prototype of whatever the noun phrase refers to. That is, it refers to one's own abstract, generalized and idealized percept of what (in this case) the roof of a car looks like and behaves. The Holy Grail of car roofs; what springs to mind when the phrase is heard or used; instantiated in English syntax.

  • A roof of a car is an Indefinite Generic, which refers to the Definition of whatever the noun phrase refers to. That is, in order to be a roof of a car, there are necessary properties; in this case, one of them is to be made of many different materials.

In effect, they imply the same thing -- pick a car, any car, and you'll find that, if it has a roof, the roof is made of many materials. So they're both grammatical; perhaps the definite generic would be more common as a strategy, in the case of the car roof. In the case of the branch, the fact that there are many branches per tree changes the prototype, but all that does is to erase any differences -- they're both fine.

If you got this question from a test, be aware that whoever made up the test is incompetent.
These are not good test questions for an English class.

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  • Oh a car has one roof but a tree has many branches. That's what't important here too! I get the branch difference. In the case of a branch, I'm a bit confused. How does it change the prototype? What difference does it erase? The branch of a tree would be wrong cos a tree has got more than one branch? – Dunno Oct 25 '13 at 7:42
  • No. It simply means that there's a rigid one-to-one relation between cars and car roofs, so you only need to be generic about one of them and the other comes with it. But with trees you have to be generic about both -- i.e, there are two acts of choosing involved. That's the change in the prototype; it doesn't affect much here. – John Lawler Oct 25 '13 at 16:03
  • oops I meant I understood the roof difference. As for the branch thing, could you possibly elaborate? What acts of choosing do you mean? Did you say "no" to the last question? – Dunno Oct 26 '13 at 10:46
  • In bib's answer, it is stated that A car roof is made of many different materials has a generic NP, whereas in The car roof is made of many different materials the NP cannot be generic but must be specific. Is this true, especially the assertion regarding the second sentence? – pazzo Oct 12 '14 at 7:20
  • If car rooves became cultural objects, like fishing rods, you could say the car roof as a generic noun phrase, because there would be a prototype for it with recognizable characteristics. As it is, car roof is simply a descriptive compound, describing any of a number of quite different objects, most of which are not distinguished from the rest of the car. Not a prototype, just a description. For a definite generic, you need a prototype. – John Lawler Oct 12 '14 at 15:05
0

They can mean the same. They can also have entirely different implications.

"A student may not absent himself without permission." -- Speaking of individual students, but uniformly applicable to the class of students.

vs.

"The student may not absent himself without permission." -- Speaking of an individual student, but not referring to the class of students.

a) A roof of a car is made of many different materials -- focus is on the roof, use when the topic is the roof.
b) The roof of a car is made of many different materials -- focus is on the car, use when the topic is the car.

Context can, and generally does, significantly influence the semantics.

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