Continuous tense

The continuous form expresses an action going on at a certain moment or for a certain period of time in the present, past or future. All the Continuous Tenses show the process of the action itself. 

Present continuous

The Present Continuous is formed by means of the Present Indefinite of the auxiliary verb to be (am/is/are) and Participle I of the no­tional verb. 

In the interrogative form the auxiliary verb is placed before the subject.

In the negative form the negative particle not is placed after the auxiliary verb.

Affirmative	Interrogative	Negative
I am reading  He is reading She is reading We are reading You are reading They are reading	Am I reading?  Is he reading?  Is she reading?  Are we reading?  Are you reading?  Are they reading?	I am not reading  He is not reading  She is not reading  We are not reading  You are not reading  They are not reading

The present continuous is used:

1) to denote an action taking place at the present moment:

a) at the moment of speaking. The moment of speaking is indicated by the adverbials: at the moment, now, at present, just now, right now, etc. e.g. The woman is wearing a white blouse and a black skirt. Nell is putting down the examples on the blackboard.

b) during the present period of time or around the present moment (in this case now obviously has a broader meaning) = a temporary situation.

The durative character of the action may be expressed by the adverbial modifiers all day/night/morning, the whole day, still, etc. e.g. They are very busy all this time, they are preparing for exams. David is collecting material for his new book now. She is working in Paris this week.

There might be two simultaneous (parallel) actions in progress: e.g. I’m writing the letter while the children are playing in the garden.

2) to denote the nearest future action which is planned or arranged. e.g. I‘m seeing Rachel tonight. We aren’t going anywhere for Christmas, we are staying at home. The construction ―to be going to‖ is often used for the same purpose. e.g. I‘m going to explore the neighbourhood.

3) to show the unusual frequency of an action in the present. It is often used with the adverbials of frequency always, constantly, never, again, etc. The speaker conveys the feeling of irritation, surprise or criticism (wants to give emotional colouring to his sentence). e.g. Mr. Stone is always grumbling. He is constantly making comments about my weight.

4) to denote actions or states having a dynamic character. = changing and developing situations. e.g. The climate is getting warmer. Mary is putting on weight. His health is improving.

5) to express a continual process. It is often used with the adverbials of frequency always, constantly, ever, etc.12 e.g. The earth is ever moving. The sun is ever shining

Some verbs do not usually have the forms of the continuous aspect.

They are referred to as state/stative verbs.

Verbs expressing sense perception: to see (видеть), to watch (смотреть), to notice (замечать), to hear (слышать), to smell (чувствовать запах), to taste (чувствовать вкус), to feel (чувствовать).

Verbs expressing emotional state: to care, to detest, to envy, to fear, to hate, to hope, to like, to love, to prefer, to want, to wish.

Verbs expressing mental state: to assume, to believe, to consider, to doubt, to expect, to find, to forget, to imagine, to know, to mean, to mind, to notice, to perceive, to remember, to suggest, to suppose, to think, to understand.

Note: Care should be taken to distinguish between some of these verbs denoting a mental state proper and the same verbs used in other meanings. In the latter case continuous aspect forms also occur. Compare, for example, the following pairs of sentences:

I consider (believe) her to be a very good student. I expected (supposed, thought) you’d agree with me. I feel (suppose) there is something wrong about him. I think (suppose) you’re right.

I’m still considering (studying) all the pros and cons. I could not come for I was expecting (waiting for) a friend at the time. I’m feeling quite cold. I am thinking over (studying) your offer

I am forgetting things more and more now (beginning to forget).

She is understanding grammar better now (beginning to understand).

Moreover, all the verbs stated above can occur in the continuous aspect when the ideas they denote are to be emphasized: Don’t shout, I'am hearing you perfectly well! Why are you staring into the darkness? What are you seeing there?