I read a book about articles and can't distinguish the difference between two rules.

A can be used to mean "any": A cat (any) is domestic animal.

The can be used when we talk about the entire category of people or objects through the name of one of them: The taxi is a car with a taxi meter.

The following is an example in which the author had in mind the meaning of any, although I think it would be possible to use the (according to the rule above): A camel can carry heavy weights.

How to distinguish these 2 rules? Then we can say the following using the same logic: A taxi (any taxi) is a car with a taxi meter.


Both these uses are comparatively rare: in Modern everyday English, it is much more common to use the plural:

Cats are domestic animals

Taxis are cars with taxi meters.

The use of the is particularly old fashioned, and hardly used except for species or breeds of animal (and, formerly, races or nationalities of people, but some find that use offensive today).

So you will find "The cat is a domestic animal", but only in old-fashioned and didactic works; but if you meet "the taxi is a car with a taxi meter" it is almost certainly talking about a specific taxi.

"A cat is a domestic animal" and "A taxi is a car with a taxi meter" are both fine, but as I say, the plural is more likely in my estimation.

  • Thanks for the reply. Is it correct to say: the computer was invented ... and a computer was invented .. I think the first is correct, and the second is not correct, isn't it?
    – Montroz
    Aug 12 '18 at 17:53
  • You can certainly use the there, @user3017797, or the plural; and you can't use a (in that sense). But I would argue that The computer was invented..., and even computers were invented... do not mean "computers in general", but "the concept or institution of the computer".
    – Colin Fine
    Aug 12 '18 at 20:39

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