Simpe present tense is used to express long lasting situations, habitual actions, truth and facts ,fixed time table and verbs of sensation , mental and emotional state. The auxiiaries do and does are used in the simple present tense to change them into negative. Now let’s look at third person sentences using he, she and it. Again, we add doesn’t between the subject and the verb to make a negative sentence.
Notice how the
letter S at the end of the verb in the affirmative sentence
(because it is in third person) disappears in the negative sentence.
Why does this happen?
The verb after the negative don’t or doesn’t is the base form of
the infinitive.
Remember, the infinitive is the verb before it is changed. To go, To
need, To speak, To live … these are all infinitives which means that
they are the original form of the verb before any changes. We know they are in
the infinitive form because of the TO at the beginning.
But for negative sentences we want the BASE form of the infinitive. This means the infinitive without TO. Instead of To go, it is just go. Instead of To speak, it is just speak.
Third person verbs lose the final S in negative sentences.
Another example:
Again you can see that in the negative sentence, speak does not have an S at the end because it is the base form of the infinitive.
Let’s see a couple more examples:
Negative Sentences with HAVE and GO
Now let’s look
at some verbs that change a little more.
The first one is the verb To Have.
But let’s look at the third person, for example with He.
Why do we use
HAVE in the negative and not HAS?
Because the verb after don’t or doesn’t is the base form of the
infinitive.
The infinitive of has is To have.
The base of the infinitive is have (without the TO at the beginning)
Let’s make
negatives sentences with the verb To Go.
To Go is the infinitive. Its base form is just Go.
We use Don’t and Doesn’t to make negative sentences in the simple present tense EXCEPT with the verb To Be and Modal verbs such as can, might, should etc. which we will see in another lesson.
Be careful…
We don’t say: I
no live in Japan. This is NOT correct.
We say: I don’t live in Japan. This is correct.
We say: She has
a cat.
We do not say: She doesn’t has a cat. This is NOT correct. We need the
base form of the infinitive which is HAVE and not has.
The correct way is: She doesn’t have a cat.
Contractions
Don’t = Do not
Doesn’t = Does not
There is no difference in meaning though we use contractions a lot in spoken English.