_.

_May_ is used (a) to show that the subject is permitted to do something,
"You may go out," or (b) to indicate possibility or doubtful intention,
"I may not go to work tomorrow."

_Can_ is used to show that the subject is able to do something, "I can
feed a press." These two forms are often confused, with results which
would be ridiculous if they were not too common to attract attention.
The confusion perhaps arises from the fact that the ability to do a
thing often appears to depend on permission to do it. "May I see a
proof?" means "Have I permission, or will you allow me, to see a proof?"
and is the proper way to put the question. The common question, "Can I
see a proof?" is absurd. Of course you can, if you have normal eyesight.

_Must_ shows necessity or obligation.

You must obey the rules of the office.

_Ought_ which is sometimes confounded with _must_ in phrases of this
sort expresses moral obligation as distinguished from necessity.

You ought to obey the rules of the office,

indicates that it is your duty to obey because it is the right thing to
do even though no penalty is attached.

You must obey the rules of the office,

indicates that you will be punished if you do not obey.

Those forms of the verb which express the time of the action are called
tenses. No particular difficulty attends the use of the tenses except in
the case of _shall_ and _will_ and _should_ and _would_.

_Shall_ and _will_ are used as follows: In simple statements to express
mere futurity, use _shall_ in the first person, _will_ in the second and
third; to express volition, promise, purpose, determination, or action
which the speaker means to control use _will_ in the first person,
_shall_ in the second and third.

The following tables should be learned and practiced in a large variety
of combinations.

Futurity Volition, etc.

I shall We shall I will We will
You will You will You shall You shall
He will They will He shall They shall

A good example of the misuse of the words is found in the old story of
the foreigner who fell into the water and cried out in terror and
despair "I _will_ drown, nobody _shall_ help me."

In asking questions, for the first person always use _shall_, for the
second and third use the auxiliary expected in the answer.

Futurity

Shall I (I shall) Shall we (We shall)
Shall you (I shall)