I came across a phrase like this today, which is obviously incorrect:

The car don't run.

The correct version of this would be:

The car doesn't run.

I wanted to explain the issue to someone, but I could not recall what property of the verb "do" is incorrect in the first sentence.

"Tense" is the first thing that comes to mind, but "do" and "does" are both in the present tense.

What is it about the word "do" that makes it incorrect?


I suppose that they could be called incorrect negative conjugations, meaning that what makes "don't" incorrect is that it has been conjugated improperly.

Correct conjugation:

The car doesn't run.

Incorrect conjugation:

The car don't run.

  • Yeah, I guess I would just say that "do" has been conjugated incorrectly. – John Gietzen Oct 24 '11 at 15:56
  • Yup: conjugation is what you do to verbs, and declination is what you do to nouns (except in English you don't do much if any declining). Both conjugation and declination are types of inflection. – Marthaª Oct 24 '11 at 16:26
  • @Martha: usually called "declension". "Declination" is something to do with geodesy. – Colin Fine Oct 24 '11 at 16:53
  • @ColinFine: dammit, that's the word I was trying to think of. Thanks! – Marthaª Oct 24 '11 at 17:55
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    @ColinFine, actually some languages use the term "declination" in grammar. Also of note, the specific conjugation error here is the wrong grammatical person. – Unreason Oct 24 '11 at 18:34

I believe you're looking for number (grammatical number), as in singular vs plural. The verb must agree in number with its subject.

In the third person ("the car"), the form does is singular, and do is plural. (So you'd say "The car doesn't run", using the singular does because car is singular, but "The cars don't run", using the plural do because cars is plural.)

|              |         Singular         |          Plural          |
|              |                          |                          |
|Third person  | does                     | do                       |
|              |      The car doesn't run |      The cars don't run  |
|Second person | do                       | do                       |
|              |      You don't run       |      You (all) don't run |
|First person  | do                       | do                       |
|              |      I don't run         |      We don't run        |

In modern English, with most verbs, it seems that the third person plural form is the same as the one used for both second and first person, in both singular and plural: only the third person singular is different. (An exception is "be", which in the first person singular is "am".)

In many other languages, all forms are usually distinct. English also had e.g. the form like "dost" that was used for (first and) second person singular ("thou dost"), which is now lost.

  • Actually, though this is slightly related more correct would be the grammatical person. – Unreason Oct 24 '11 at 18:33
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    @Unreason: Isn't the car third-person in both sentences? Does person include number too, these days? – ShreevatsaR Oct 24 '11 at 19:20
  • the way I learnt it, it was always like that (hence the full names such as first person singular, third person nutral singular, see en.wikipedia.org/wiki/…), furthermore grammatical person is specific to verb forms, where grammatical number deals with arrangement of nouns, pronouns, adjectives and verbs. – Unreason Oct 24 '11 at 19:32
  • @Unreason: The way I learnt it, "person" just refers to first/second/third person… and person, number and tense(/aspect/mood) are three independent axes for a verb form; that's why the full names like "first person singular" specify both the person and the number. But under the way you learnt it, what is the name for just what I called "person", namely first/second/third? – ShreevatsaR Oct 25 '11 at 5:05
  • Ok, I see your point; TEFL wiki talks about 3 persons in singular and 3 persons in plural (i.e. includes the number in the person, teflworldwiki.com/index.php/Grammatical_Person); while about.com does not (grammar.about.com/od/pq/g/personterm.htm). Overall it seems you are more correct; however I think you should have mentioned the person, as it is imprecise to say: 'does is singular (true, but imprecise; more precise to say is that it agrees with third person singular), and do is plural (false; it agrees with all other persons; singular or plural)'. – Unreason Oct 25 '11 at 7:29

In Standard English, the present tense of the auxiliary verb do in the negative is don’t (contracted from do not) when the subject of the sentence is I, you, we or they. When the subject is he, she or it, it takes the form doesn’t (does not). In your example, the car could be replaced by it, so Standard English requires the sentence to be The car doesn't run.

(That’s the case with Standard English. The grammar of some other dialects is different and would allow The car don’t run.)

  • And in the 1880's British prestige dialects appear to have allowed it, judging from W S Gilbert – Colin Fine Oct 24 '11 at 16:54
  • That might make an interesting piece of research. – Barrie England Oct 24 '11 at 18:57

The difference is obvious if you undo the contraction: doesn't == does not, and don't == do not.

Then, you see that the difference is in conjugations of the verb "to do" in the present tense, which differs based on the subject (notably in use of the third-person singular):

  • I do

  • You do

  • He/She/It does

  • We do

  • They do

So when referring to one single thing that is not a participant in communication (a "third person"), you use "doesn't". In all other cases, use "don't".

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