When discussing a nondescript apple, a nondescript taxi, and a nondescript book borrowed from a nondescript library, which article is more natural and grammatically correct in each of these sentences? If either is fine, are they equally natural and grammatically correct or do you have a preference?

  1. When an apple falls from [a/the] tree, it necessarily falls to the ground.
  2. I took a taxi here, but [a/the] driver was so unfriendly.
  3. I’ve got a book I need to return to [a/the] library.

A tree? Why? It’s impossible for an apple to have come from several trees. There’s always one unique tree associated with each apple. Doesn’t that mean that an apple falling fell from the tree that bore it, and thus that the definite article is necessary?

The tree? Why? It’s an apple that comes from/was borne by a tree. why does it suddenly need the definite article?

A driver? Why? The same way choosing an apple pins down a tree as the tree, doesn’t choosing a taxi also pin down the driver? So it should be the driver that drove it, no?

The driver? Why? The taxi was driven by a driver. also if you think ‘…from a tree…’ sounds okay but ‘…a driver…’ doesn’t, why is that?

A library? Why? For each book borrowed from a library, there’s always one unique library associated with it, the library it came from. and that’s the one you should return the book to. no?

The library? Why? Isn’t the library the book came from a library? It’s a library and you’re returning a book to it, i.e., to a library. So why the definite article?

What are the rules? And how does meaning change based on which article I choose?


5 Answers 5


In your sentences the position of [a/the] was different in sentence 1 from its position in sentences 2 and 3.

The following sentences have the articles in both positions.

  1. When an apple falls from a tree, it falls to the ground below the tree.
  2. I found a taxi with a driver, but the driver was unfriendly.
  3. I’ve got a book from a library, and I need to return it to the library.

In each of these examples the first italicised article is a, while the second is the. We can use the because tree, driver or library has already been mentioned.

Now consider the following sentences.

  1. When an apple falls, it falls to the ground below the tree.
  2. I found a taxi, but the driver was unfriendly.
  3. I’ve got a book, and I need to return it to the library.

Your argument for the is correct in all three of these cases. The identities of the tree, driver and library are implied by the earlier parts of the sentence.

Now consider the first parts of my earlier sentences. There is no previously mentioned or implied tree, driver or library; until they are mentioned the apple could just easily have fallen from a table, the driver could be any from a pool of drivers, and the book could have come from a shop. Because a hearer need not identify which tree, driver or library is now being mentioned, using a is correct.

We use the when we want (or need) to be specific about something. Sometimes context (not always written) provides the information.

Consider the sentences written with the definite articles.

  1. When an apple falls from the tree, it falls to the ground below the tree.
  2. I found a taxi with the driver, but the driver was unfriendly.
  3. I’ve got a book from the library, and I need to return it to the library.

Sentence 1 will usually be understood, as you thought, to be referring to the apple's tree. However, if you have just watched a bird in an oak tree your hearer may at first expect you to be talking about that tree.

Sentence 2 is actually awkward; the first part suggests that you had already identified the driver and you found a taxi that he/she was driving.

Sentence 3 will usually be understood as referring to a specific library, for example your local library.

  • thanks for the detailed explanation – i understand it much better now. one follow-up: does an apple not fall far from a tree or the tree? (assume the sentence is not said figuratively and you’re not referring to a certain parent as the tree) my (unskilled) intuition wants the. but could you please elaborate how your logic applies to this example?
    – potato
    Commented Jan 13 at 10:59
  • 1
    It is the apple doesn't fall far from the tree. The definite article makes it clear that a specific tree is intended, and the sentence itself establishes enough context to identify the tree. For many English speakers there is cultural context as well to add another meaning.
    – Peter
    Commented Jan 13 at 11:36
  • yeah that‘s why i added the disclaimer about this not being about a specific parent or anything like that. but from a purely physics perspective (the purely physics perspective?), wouldn’t an apple be better than the apple?
    – potato
    Commented Jan 13 at 12:48
  • There are statements like "the elephant is a large animal" where "the" is used generically. The first ""the" in "the apple doesn't fall far from the tree" is used this way. There are several questions about generic uses of "the". See for example ell.stackexchange.com/questions/22647/… .
    – Peter
    Commented Jan 14 at 2:07

As a general rule the definite article is for something specific while the indefinite article is for something general, or generic.

For example, "the apple in my lunchbox is rotten" uses the definite article because you are speaking about a specific apple, the one in your lunchbox, and something has happened uniquely to that apple. However, we would say "there is an apple in my lunchbox" because it could be any apple in there - any one you happened to pack, any variety of apple - it is generic because you're not saying anything specific about it and it doesn't matter to your statement.

However, we do sometimes use the definite article for something generic. The most commonly-cited example is when referring to animal species - we might say "the elephant is the largest land animal", even though this statement refers to elephants in general.

In your example of "an apple falls from a/the tree", either article could work. As you are referring to a non-specific apple, it can be a non-specific tree; but it also works with the definite article for the tree because any individual apple can only fall from one tree - the one it grows on. Interestingly, there is a well-known proverb "the apple never falls far from the tree" which uses the generic 'the' for both apple and tree and of course has a general, proverbial, application. Other proverbs, such as "a leopard never changes its spots" work the same way with the indefinite article.

Your other examples aren't necessarily directly comparable. It should be the driver because, while you may have booked any particular taxi, you are making a statement about the specific driver you ended up with. And it should be the library, because libraries are public buildings like hospitals, theatres, town halls etc, and as another general rule we tend to refer to them with the definite article (eg "I went to the theatre", or "I ended up in the hospital").

  • 1
    Very comprehensive and accurate answer. Except perhaps that in the last example about "the hospital", in Britain we use no article at all, saying "she ended up in hospital". Similarly "he ended up in prison/college/etc.
    – WS2
    Commented Jan 15 at 15:14
  • @ws2 Being British myself I'm aware of that and I was hoping not to get into that debate and confuse the answer! But that peculiarity only applies when speaking about being admitted. We would still say, for example, "I work in the hospital" to mean the one in our area. That example would be wrong without an article, and using the indefinite article would probably prompt the follow-up question of "which one?"
    – Astralbee
    Commented Jan 15 at 15:58
  • what about this sentence: ‘the electric potential at a point is the amount of energy needed to move [a/the] unit charge from a reference point to that point’? i think a might work because it’s discussing the amount of energy needed to move one unit of charge, whatever unit you might be using. i think the might also work because, since we aren’t using multiple units at a time, it could be understood to be referring to the unit of choice of the reader/listener. if you were to open a new chapter with this sentence, ie there’s no context, which would you choose?
    – potato
    Commented Jan 16 at 2:06
  • @Astralbee I think there is an extensive post on this subject either on this site or EL & U. Without an article it describes not so much where the person is but their status. If you are "in hospital" it is simply saying that at the moment you are hospitalised, similarly "in prison" you are a convict., or "in school" you are a pupil. However people work in a/the school, a/the hospital, or a/the prison.
    – WS2
    Commented Jan 16 at 15:08
  • @potato I think that is too highly technical to be asked here. Let's dumb it down: The boy at a [a/the] mile marker on the road is the boy needed to drive [a/the] tractor from [the/a] farmhouse to that point. You seem to be limiting the a/the you ask about. I suggest you master an easier example first.
    – Lambie
    Commented Jan 16 at 15:10

When an apple falls from [a/the] tree, it necessarily falls to the ground.

I took a taxi here, but [a/the] driver was so unfriendly.

I’ve got a book I need to return to [a/the] library.

Good examples.

Any apple, it's merely an example, hence "an apple". Which tree has no relevance, hence "a tree", but you can make the example more "concrete" or more "proverbial/universal" with "the tree".

One of many taxis, hence "a taxi". A taxi has a driver, its driver, hence "the driver".

One of many books, which one is not relevant, hence a. Which library is also not relevant, but we're not talking about one of many libraries; rather we are talking about a generic-bordering-on-universal task, and we express genericity/universality with the. For example: He's in the hospital (he's hospitalized); Uh oh! I'm in the dog-house (I've made someone who is close to me or in my family angry with me); It was lost in the mail (the never-ending flow of letters and parcels).

  • The grandfather told Anna: When an apple falls from the tree over there, etc.//A taxi not one of many taxis. It is not an elephant or truck.
    – Lambie
    Commented Jan 14 at 20:07
  • You say "a taxi is one of many taxis". That is simply not true. It can be several things and one needs context to say one way or another. And I'd try hard not to get into personal comments. In my 35 years of translating, editing. proofreading and teaching English, I find that people commenting on things revert to personal comments when they simply are unable to pursue a complicated discussion, which, it's true, can become very involved.
    – Lambie
    Commented Jan 14 at 22:30

perhaps, an over-simplification for this use:

a = any/vague/multiple possible objects or subjects,

the = one/specific/a previously agreed upon object or subject.

  1. an apple can fall from any tree/a tree. an apple that falls from the tree speaks specifically to one tree, not all the trees that bare apples. however, in the context of an apple falling, it would not make sense to point to a specific tree unless discussing an aspect of one particular tree that made an apple falling from that tree uniquely different from any other apple falling from any other tree.

  2. a specific taxi was taken. this points to a specific driver/the driver. if it was any driver we would use a driver. but, this becomes confusing, as you've already mentioned taking a specific taxi; indicating a specific driver. a driver potentially indicates more than one driver of the same taxi.

  3. again, here, a library does not indicate to which library the book should be returned. it could be any library. the library indicates the holder of this book knows which library to visit. now, I believe in this last example, the use can go either way. if the speaker wanted to be intentionally vague... a library is not only appropriate, but reveals more context.

  • a = any/vague/multiple possible objects or subjects, Do you have a car? Means one.
    – Lambie
    Commented Jan 14 at 20:04

"Examples you can use"

  1. When an apple falls from a tree, it necessarily falls to the ground. [OKAY]
  2. When an apple falls from the tree outside my window, it falls into the pool. [okay]

WHY? Because 1) is a general statement and 2) is specific.

However, the cliché or idiom people use in speech is: The apple doesn't fall far from the tree.

WHY? Because it is the specific tree from which the apple fell. This is used to describe people or the actions compared to another person.


  • I took a taxi here, but the taxi driver was so unfriendly.
  • He bought a brand-new red car. The car seemed so big!

The determiner a shifts to the on the second mention of the noun. A taxi becomes the taxi driver. It is now specific.

Bear in mind: forms of transportation idiomatically take either determiner:

  • I came on the bus, not the train.

  • I came on a bus, not a train.

  • I took the plane, not a car.

  • I took a plane, not a car. [a or the for those] For these, the the is still specific and the a is still general. You have to feel the difference. Forms of transportation (car, bus, train, plane are often used with the)

  • I’ve got a book I need to return it to the library.

Books are borrowed from specific libraries near where one lives (as in the sentence above). They cannot be returned to a library but to the library where they were borrowed.

Borrowing a book at a library can be time consuming.
That's a general statement.

General rule: the a determiner is always general; the the determiner is always specific.

The lion is a noble beast.=Follows the specific rule and is more formal than: Lions are noble beasts. The the is used in the same way that the plural is used to show a general case, formally.

Not every usage of a/the can be covered in this answer.

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