When should I use "a" or "the" to talk about something in general?

The first example:

The computer has revolutionized

A computer has revolutionized

The second example:

The computer is an important research tool

A computer is an important research tool

Can someone explain the difference in meaning between these two sentences?

  • For the generality, I'd use computers have revolutionized for the first two. And A computer is an important research tool. for the second two.
    – Abbasi
    Commented Dec 31, 2016 at 15:43
  • I would also like to see the answer for "Dog is our good friend" (dog in general, as in all dogs are our good friends). Suppose that it is like the second example "A? computer is an important research tool" Commented Dec 22, 2021 at 8:09

1 Answer 1


For your first example

The computer has revolutionized

is correct. That is, it is computers in general, not a specific computer that has changed life as we know it.

For your second example, I think either works, although I lean towards "A computer ...". I'd be interested to see what others say.

  • The first example is just more obvious. A generic statement always take the definite article 'the'. 'A computer can be…' for instance, isn't truly generic; it's a specific example being used to illustrate a general idea. Commented Jan 12, 2017 at 1:27

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