Will / Might
Expressing Degrees of Uncertainty
Present & Future Uncertainty (Prediction)

VERY CERTAIN	UNCERTAIN	UNCERTAIN NEGATIVE
Polar bears will perish.	Polar bears may perish.	Polar bears may not survive.
Polar bears are going to perish.	Polar bears might perish.	It is doubtful that polar bears will survive.
	Polar bears could perish.	It is unlikely that polar bears will survive.
100 % degree of certainty	less certain	uncertain

Will / Would

Expressing Intent, Expectation, Refusal and Disappointment

Intent vs. Expectation

WILL – INTENT	WILL – EXPECTATION
Use will to express determination to do something. (volition)	Use will to indicate that something is scheduled, expected to happen, or is a predictabe, reoccurring event.
Next month, I will get a raise in salary. (I am  determined to do so.)	Next month, I will get a raise. (It's scheduled in my contract.)
I will try harder to achieve my goals. (I am  determined to do so.)	Next month, I will get a raise. (I expect to; I've worked so hard.)
Our team will win the championship!  (We set our minds to it.)	Our team will win the championship!  (We expect to because we've done well so far.)

Would

Stating Preference, Request, Habit or Excuse

Preference vs. Request

PREFERENCE - DESIRE	REQUEST
Would you rather  X than Y.  Would you rather X or Y? are expressions stating preference.	Would you  or Would you mind (if) are polite ways to state request.
I would rather have my breakfast outside than inside.	Would you like having breakfast outside?
We would rather eat fish tonight than meat.	Would you suggest some wine to go with our fish dish?
I would rather smoke indoors than outdoors.	Would you mind if I smoke inside?
I would rather you smoke outdoors than indoors.	Would you mind not smoking in here? (expression following by gerund)
I would rather you not smoke here.	Would you not do that please.
We would rather have our coffee before than after our dessert.	Would you please bring me some coffee.

 Should

Expressing Expectation, Convention or Advice

 

Expectation

SHOULD	WILL
Should is used for a logical assumption or expectation.	Will is also used for an expected, predicted or scheduled event.
The movie should be available next week.	The movie will be available next week. (This is what I expect.)
It's noon.  The mailman should be here any minute.	It's noon.  The mailman will be here any minute.
Movie fans should be excited to see the James Bond movie.	Movie fans will be excited to see the James Bond movie.

  

Convention

SHOULD	(BE) SUPPOSED TO
Should is used to indicate a cultural expectation or norm for behavior.	Supposed to is also used to indicate a cultural expectation or norm for behavior.
People should be honest and not steal creative work.(ethical convention)	People are supposed to be honest and not steal creative work.(ethical convention)
People shouldn't talk on cell phones during movies. (convention)	People aren't supposed to talk on cell phones during movies. (convention)
Should we wear black pants to work? (convention)	Are we supposed to wear black pants to work?(convention)

  

Options or Advice

SHOULD	OUGHT TO
Should is used for giving options or advice.	Ought to is also used for giving options or advice.
You should try ordering your movies online.(option)	You ought to try ordering your movies online.(option)
He should ask one of his professors for a recommendation. (option)	He ought to ask one of his professors for a recommendation. (option)
She shouldn't talk on her cell phone when she's with you. (advice)	She ought not to talk on her cell phone when she's with you. (advice)

 

Could / Should

Problem Solving

  

Offering Help vs. Giving Advice

COULD	SHOULD
Could states an option or a suggestion – other options to try.	Should states advice, a stronger suggestion - the best option to do.
"I lost my wallet. What am I going to do?"     "Well, you could . . .  go back to the last place you saw it. check the lost and found. remember where you went today. search your house and car.	"I lost my wallet. What am I going to do?"     You should . . . cancel your credit cards. notify the campus police.

Should / Must

 Expressing Advisability

 

 

 

Whether something is "advisable" or "necessary" often depends on one's point of view.

In the sentences below, an "environmentalist" would use "must", whereas another person might use "should".

 

Present - Should vs. Must

SHOULD	MUST
ADVISABLE    (a good idea)	NECESSARY (imperative)
We should protect our environment. It makes good sense.	We must protect our environment, or our resources will disappear.
We should select cars that are more fuel-efficient.	The car industry must change engines that burn fossil fuels.
We should use re-usable bags when shopping.	Stores must give out recyclable plastic bags.

 

Other Expressions

OUGHT TO / IT'S A GOOD IDEA	HAVE TO
ADVISABLE    (a good idea)	NECESSARY (imperative)
I ought to install solar panels on my roof.	We have to use more alternative energy sources.
You ought not to use your fireplace very often.	Everyone hass to save energy.
It's a good idea to leave your car in your garage.	People have to make changes in their habits.

Must / Must have

Conclusions

 

 We often try to guess what is happening in a situation that we see.  Might is used for guesses.

With a little more background information we can better judge what is happening.  Must is used for making conclusions.

 

Guessing vs. Concluding

MIGHT  HAVE	MUST HAVE
A guess based on a little information	An informed guess (conclusion, inference, deduction) based on more information.
She's sad. She might miss her family or she might be disappointed.	Also, she is alone. She has nothing but a glass of absinthe (strong alcohol). She must be depressed.
He looks tired.  He might be working late or he might be partying at night.	Also, he is handing his boss the annual report. He must have been working late last night to finish the report.
The farmer's market had no plastic bags.  They might have been out of bags.  They might have expected customers to bring their own bags.	Also, other people in the market had their own bags.   The market must have expected people to bring their own bags.

 

 

 

Other Expressions

OUGHT TO / IT'S A GOOD IDEA	HAVE TO
ADVISABLE    (a good idea)	NECESSARY (imperative)
I ought to install solar panels on my roof.	We have to use more alternative energy sources.
You ought not to use your fireplace very often.	Everyone hass to save energy.
It's a good idea to leave your car in your garage.	People have to make changes in their habits.

 

Can / Could

 Expressing Ability

  

Can expresses four types of ability:

PHYSICAL ABILITY	MENTAL ABILITY	POTENTIAL ABILITY	ABILITY TO SUCCEED IN REACHING A GOAL
The Internet can transfer video files onto personal computers.	People can find use computers.	Contestants can become famous after appearing on American Idol	I was able to buy an iphone after saving for two months. (Used for a single occurrence, a moment of completion or success; cannot use could)

 

 

 

Physical Ability

CAN	BE ABLE TO
To have the physical ability.	To have the physical ability.
High-speed connections can download large music files in seconds.	High-speed connections are able to download large video files in seconds.
People can exercise to lose weight.	People are able to exercise to lose weight.
Smart phones can connect to the Internet.	Smart phones are able to connect to the Internet.

 

Mental Ability

CAN	KNOW HOW TO
To have the mental ability or capacity	To have the mental ability or capacity
We can solve our economic problems	We know know how to solve our economic problems.
Engineers can design safer buildings.	Engineers know how to design safer buildings.
Farmers can grow pesticide-free fruit and vegetables.	Farmers know how to grow pesticide-free fruit and vegetables.

 

Potential Ability

CAN	HAVE POTENTIAL
To have the possibility of; be capable of becoming	To have the possibility of; be capable of becoming
Overspending can crash the economy of a country.	Overspending potentially crashes the economy of a country.
Overeating can cause diabetes.	Overeating potentially causes diabetes.
Singing contestants can become famous by appearing on American Idol.	Singing contestants potentially become famous by appearing on American Idol.

 

 

An Ability to Succeed

COULD	WAS ABLE TO
*Not used.  Could is used for multiple occurrences, habitual activity.	Used for a single occurrence, a moment of completion or success; "manage to"
*I practiced a lot and by fall, I could get my driver's license.	I practiced a lot and by fall, I was able to get my driver's license.
	Through hard work and excellent research, they were able to find a cure for the disease.
	After saving for five years, they were able to buy their own home.

May / Can

Requesting Permission and Offering Suggestions

 

Giving permission, making requests and offering suggestions require the speaker to be aware of levels of formality.

Some expressions are used with persons of authority and with people whom we are unfamiliar while others are used with peers and people with whom we are familiar.

 

 

Permission

MORE FORMAL	LESS FORMAL
May I smoke here? You may use your cellphone in the restaurant patio.	Can I smoke here? You can use your cellphone in the restaurant patio. (less formal; an option)

 

 

 

 

 

 

 

Request

MORE FORMAL	LESS FORMAL
Would you please smoke outside? Would you mind smoking outside please?	Will you smoke outside please? Can you smoke outside please? Could you smoke outside please? Do you think you could smoke outside? I'd like you to smoke outside please.   (would like)

 

 

Suggestion / Invitation

MORE FORMAL	LESS FORMAL
Shall we go outside? Would you mind smoking outside please?	Let's go outside? Why don't we go outside? How about going outside?