MAY - to be allowed (permitted) to do smth.

  1. CAN - be able to do smth. / Be capable of doing smth.
meaning use present past
1. permission + /? You may use my ISP if you wish. -
2. prohibition - You may not use my e-mail box. -
3. possibility + / - It may / might be a faulty program. The modem may / might not have been switched on.
4. suggestion + We might use other graphical software. -
5. complaint + They might pay more attention to the instructions. He might have checked his e-mail at least sometimes.

Notes:

1. Mayhas only two tense forms: may(Present) and might(Past), so for other tenses to be allowed (permitted) to do sth.is used.

2. Mightis not always the past of may, Sometimes it has a present or future meaning. Perfect infinitive after mayor mightin such cases shows that they refer to the past.

3. Passive and progressive infinitives after mayor mightare also possible in some cases.

2. , 䳺may :

1. This device may not be switched on here. 2. At first the desktop might seem a little foreign to you. 3. It's also more installation procedures than you might expect. 4. Will she be allowed to process these figures? 5. It may have beensaid that the development of modern computers was entirely depended upon developments in integrated circuits. 6. Different combinations of 1s and 0s may be used to represent numbers and characters (letters of the alphabet special characters). 7. Were they allowed to operate that new device? 8. Programs other than the one that is being obeyed may be stored on a backing-store external to the computer memory. 9. You may not be the only person using the program and this is the factor to be considered. 10. Combining both of these technologies might produce a completely new range of possibilities for user of information technology.

MUST

meaning use present past
1. obligation (speaker's authority) +? They must provide us with all necessary data. -
2. necessity (speaker's thought) + He must work hard to learn this computer language. -
3. prohibition - You must not press any button. -
4. certainty + He must be working in the Internet. I can not call him. They must have already opened this file.

Notes:

1. Musthas no other forms. To express past perfect infinitive can be used sometimes.

2. Had tois the past form of mustwhich refers to a past obligation.

3. Needis used in its negative form to express the lack of necessity.

3. , 䳺must :

1. The data must have been lost. I do not see it anywhere. 2. To use a CD-ROM, you must have a computer equipped with a CD-ROM drive. 3. You must not interfere with the program work. 4. To read this graphics file you must have used a program that recognized the file's format. 5. The user must create sample input data that represents every possible way to enter input.



CAN - be able to do smth. / Be capable of doing smth. | SHOULD / OUGHT TO

| | | | II. | III. | II. | HAVE TO | WILL / WOULD | Design for Decision |

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