Should / Must
Expressing advisability and necessity
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 |
|---|---|
Use ought to or It was a good idea to ... for past advice. |
Use had to or needed to or It was necessary that ... for past necessity. Use had to for actual past events. |
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 had to save energy. (and they did.) |
It's a good idea to leave your car in your garage. |
People have to make changes in their habits. |
Past - Late Advice vs. Past Necessity
| SHOULD HAVE | * MUST HAVE |
|---|---|
Use should have for advice given after the event happened. "It was advisable, but did not happen." The advice is hypothetical – what we would have done in a particular situation. |
Use had to or needed to or It was necessary that ... for past necessity. Use had to for actual past events. Must have is used for making conclusions not for stating past necessity. |
We should have protected our environment. (but we didn't.) |
We must have protected our environment. (*Must have means conclusion not necessity.) |
We should selected cars that were more fuel-efficient a long time ago. (but we didn't.) |
|
We should have banned the use of plastic bags. (but we didn't.) |
|
Other Past Expressions
| OUGHT TO HAVE | HAD TO |
|---|---|
It was advisable, but did not happen. (Advice that comes too late to use.) |
It was necessary. |
I ought to have installed solar panels on my roof. (but I didn't.) |
We needed to use more alternative energy sources to save money. |
You ought not to have put in a lawn in your yard. (grass) (but you didn't.) |
Everyone needed to save energy during the hot summer. |
It would have been a good idea to use plants that didn't need much water. |
It was necessary that we used plants that required little water. |
Sentence
Word Order
| SENT. TYPE | AUXILIARY VERB | SUBJECT | AUXILIARY VERB | VERB BASE / INFINITIVE | TAG CLAUSE | |
|---|---|---|---|---|---|---|
STATEMENT advisable |
|
We |
should |
select (verb base) |
energy-efficient cars. |
|
advisable |
|
We |
ought |
to select (infinitive) |
energy-efficient cars. |
|
necessary |
|
We |
need |
to select |
energy-efficient cars. |
|
necessary |
|
We |
have |
to select |
energy-efficient cars. |
|
QUESTION advisable |
Should |
we |
|
select |
energy-efficient cars? |
|
advisable |
Ought |
we |
|
to select |
energy-efficient cars? |
|
necessary |
Do |
we |
need |
to select |
energy-efficient cars? |
|
necessary |
Do |
we |
have |
to select |
energy-efficient cars? |
|
TAG QUESTION advisable |
|
We |
should |
select |
energy-efficient cars, |
shouldn't we? |
advisable |
|
We |
ought |
to select |
energy-efficient cars, |
oughtn't we? |
necessary |
|
We |
need |
to select |
energy-efficient cars, |
don't we? |
necessary |
|
We |
have |
to select |
energy-efficient cars, |
don't we? |
NEGATIVE advisable |
|
We |
shouldn't |
select |
energy-efficient cars. |
|
advisable |
|
We |
ought not |
to select |
energy-efficient cars. |
|
necessary |
|
We |
don't need |
to select |
energy-efficient cars. |
|
necessary |
|
We |
don't have |
to select |
energy-efficient cars. |
|
W / ADVERB advisable |
|
We |
should continually |
select (verb base) |
energy-efficient cars. |
|
advisable |
|
We |
ought to knowledgeably |
select (verb base) |
energy-efficient cars. |
|
necessary |
|
We |
need to carefully |
select (verb base) |
energy-efficient cars. |
|
necessary |
|
We |
have to responsibly |
select (verb base) |
energy-efficient cars. |
|
A tag question can also occur with a negative main sentence and a postive final question: They shouldn't do that, should they? (I don't think they should.) Related page: And so / too
Not Required vs. Prohibited
| DON'T HAVE TO | HAVE TO NOT |
|---|---|
Use don't have to if something is not required. |
Use have to not if something is prohibited. |
You don't have to park on the street. It's not necessary. |
You have to not park on the street. It's necessary not to. |
He doesn't have to go to work everyday. He can work from home. (It's not necessary.) |
He has to not miss a minute of work. He's an airplane flight controller. |
We don't have to drive big cars. |
We have to not drive big cars. |
Practice 1
Store Return Policy
- Select your response from each menu.
- Then check your answer.