a) Study this explanation and compare the examples:
- Present Continuous (I am doing)
Use the present continuous tot talk about something which is happening at or around the time of speaking.
~ The kettle is boiling. can you turn it off, please?
~ Listen to those people. What language are they speaking?
~ 'Where's Tom?' 'He's playing tennis.'
~ (you find a stranger in your romm) What are you doing here?
~ Silvia is in Britain for three months. She's learning English.
Use the present continuous for a temporary situation:
- I'm living with some friends until I can find a flat.
- that machine isn't working. It broke down this morning.
- Present Simple (I do)
Use the present simple to talk about things in general or things which happen repeatedly
~ Water boils at 100 degrees Celcius.
~ Excus me, do you speak English?
~ Tom plays tennis every Saturday.
~ What do you usually do at weekends?
~ What do you do? (= What's your job?)
~ Most people learn to swim when they are children.
Use the present simple for a permanent situation:
- My parents live in London. They have been there for 20 years.
- That machine doesn't work. It hasn't worked for years.
b) Some verbs are used only in simple tenses. For example, you cannot say ' I am knowing '. you can only say I know. here is a list of verbs which are not normally used in continuous tenses (but there are exceptions):
want like belong know suppose remember
need love see realise mean forget
prefer hate hear believe understand seem
have (when the meaning is 'possess')
think (when the meaning is 'believe')
~ Do you like London? (not 'are you liking?')
~ He doesn't understand. (not 'he isn't understanding')
~ These shoes belong to me. (not 'are belonging')
~ What do you think Tom will do? (= What do you believe he will do?)
but: What are you thinking about? (= What is going on in your mind?)
Thanks to Cambridge University Press, "English Grammar in Use"