Possibility:

We use may, might or could when something is possible.

      It may rain.

      It might not rain.

      Scientist could find a cure for cancer in the next 20 years. 

Certainty:

When we are sure that something certain we use must.

      I have eaten a lot these holidays.

When we are certain that something is not possible or it is impossible, we use can’t.

      All the lights are off. She can’t be at home.

Practice them:

http://www.englishexercises.org/makeagame/viewgame.asp?id=2083

http://www.englishexercises.org/makeagame/viewgame.asp?id=5901

http://www.englishexercises.org/makeagame/viewgame.asp?id=5570

“If you can’t, you must. If you must, you can.”     

Modal verbs are a type of auxiliary verb. These are their characteristics:

• They are accompanied by verbs in the infinitive without “TO”.

                Police officers must wear a uniform - Police officers must to wear a uniform

• They have the same form for all the persons (we don’t add -s to the 3rd person singular):

                   She can play the piano - She cans play the piano - She can plays the piano

• They don’t need auxiliary verbs:

                    They shouldn’t stop smoking - They don’t should stop smoking

                     Can you do it? - Do you can do it?

• They are different from auxiliary verbs because they add meaning:

                    You may win the lottery (it is possible that you win the lottery - possibility)

                    He can drive (he has the ability)

Here you have some links to practise the difference between these two verbal tenses. I hope they are useful and helpful.

http://www.aulafacil.com/Ingejerc/Lecciones/Ejerc21.htm

http://www.ego4u.com/en/cram-up/grammar/prepersim-preperpro 

http://www.englishgrammarsecrets.com/presentperfectsimpleorcontinuous/menu.php

http://www.usingenglish.com/quizzes/154.html

http://learnenglish.britishcouncil.org/en/grammar-reference/present-perfect-simple-and-present-perfect-continuous

 If you have any doubt, feel free to leave a comment or ask me in class.

Are you good at writing? Do you like telling stories? This activity is for practising the Past forms. Leave a comment continuing the beginning of the story. You can’t use more than 50 words. Be original and creative!

 Yesterday, I got up very early and when I went into the kitchen…