OK, this will get a bit complicated. Are you ready for this?
There are different types of verb. You can have main verbs, which describe actions (play, sing, write); auxiliary verbs, which help with the grammar; and modal verbs, which describe possibility or permission (can, will, may).
The modal verbs are do, have and be. We use have, for example, to build the present perfect. Take this sentence:
Peter has made a cake.
Here, "has" doesn't mean anything at all. The action is described with "made", which comes from "make", and that's the main verb. "Has", from "have", is only there to help with the grammar.
Modal verbs also count as auxiliaries -- in fact, they are often called "modal auxiliaries":
Peter can make cakes.
Here, "make" is the actual action: "can" just indicates that Peter has the ability to do that thing.
When we want to make a negative, we put the word "not" after the auxiliary verb, like this:
Mary is playing the saxophone. -> Mary is not playing the saxophone.
Gordon has written a letter. -> Gordon has not written a letter.
I can see for miles. -> I cannot see for miles.
That's simple, but what happens in a tense like the present simple or the past simple, where there is no auxiliary? "We bake bread" -- no auxiliary to put "not" after. In that case, the auxiliary "do" comes to our aid. It arrives, like Superman, to help out when no other auxiliary verb can help:
We bake bread. -> We do not bake bread.
The same is true of questions.
This explains why:
I have got a dog -> I do not [or: don't] have a dog.
"Have" is an auxiliary, and "got" is the main verb.
But that doesn't explain:
I have a dog. -> I don't have a dog.
Shouldn't that be, "I haven't a dog"?
Well, in informal speech it can be, and in fact some native speakers do say it that way. But strictly speaking, the construction with "do" is more logical. But why should we? Isn't "have" an auxiliary?
The answer is: Not always. "Have" can sometimes be a main verb: it means the same as "possess". So in this case, when "have" actually means something, we use "do".
In the same way, "do" can also be a main verb:
I did my homework. -> I did not do my homework.
Here, we have to add another "do", because in the original sentence "did" (the past tense of "do") is actually a main verb.
That's why the traditional, formal greeting "How do you do?" has "do" twice: the first is an auxiliary needed because we have to make a question; and the second is the main verb.
"Be" is a special case. You can always put "not" after "be": I am not German.
Which is better? Well, when it means "possess" or "must", we can use either "have" as a main verb, or we can use "get" as the main verb in the present perfect, "have got" -- both are correct. But "have got" is used more in Britain than in the US, and it sounds a little bit less formal.
thanks a lot.
this was useful.
it is a little bit funny for me the thing that for example a word is used in British English and other in American English.
the problem in Romania is that we don't learn let's say British Engl. or Amer. English. we mix them. the accent too. so sometimes I have to explain to myself we a word or a phrase is used more often than other. te explanation is that there is Br. English and. Amer. Engl.