We can use have to + infinitive, must + infinitive and should + infinitive to express obligation (something you have to do).
Present
Positive
Negative
have to / don’t have to
strong obligation (possibly from outside)
Children have to go to school.
(sometimes ‘have got to’)
no obligation
I don’t have to work on Sundays.
You don’t have to eat anything you don’t like.
must / mustn’t
strong obligation (possibly based on the speaker’s opinion)
I must study today.
negative obligation
You mustn’t smoke here.
should /
shouldn’t
mild obligation or advice
You should save some money.
mild negative obligation or advice
You shouldn’t smoke so much.
Be careful about the difference between mustn't and don't have to! Mustn't means it's not allowed, or it's a bad idea:
You mustn't eat so much chocolate, you'll be sick
Don't have to means you don't need to do something, but it's fine if you want to do it:
I don't have to get up early at the weekend (of course, if I want to get up early, that's fine, but I can stay in bed if I want
Past
Positive
Negative
had to / didn’t have to
obligation in the past
I had to go to wear a school uniform when I was a child.
no obligation in the past
We didn’t have to go to school on Saturdays.
must*
changes to 'had to'
-
should have + pp / shouldn’t have + pp
a past action which didn’t happen: the advice / regret is too late
You should have gone to bed earlier, now you have missed the train.
a past action which didn’t happen: the advice / regret is too late
You shouldn’t have taken that job., it was a bad idea.
* Remember ‘must have done’ is a modal verb of deduction or speculation, not obligation in the past.
For example: Julie must have left. Her coat’s not here.
Form the comparative and superlative forms of a one-syllable
adjective by adding –er for the comparative form and –est for the
superlative.
One-Syllable Adjective
Comparative Form
Superlative Form
tall
taller
tallest
old
older
oldest
long
longer
longest
Mary is tallerthan Max.
Mary is the tallestof all the students.
Max is olderthan John.
Of the three students, Max is the oldest.
My hair is longerthan your hair.
Max's story is the longeststory I've ever heard.
If the one-syllable adjective ends with an e, just add –r for the comparative form and –st for the superlative form.
One-Syllable Adjective with Final -e
Comparative Form
Superlative Form
large
larger
largest
wise
wiser
wisest
Mary's car is largerthan Max's car.
Mary's house is the tallestof all the houses on the block.
Max is wiserthan his brother.
Max is the wisestperson I know.
If the one-syllable adjective ends with a single consonant with a
vowel before it, double the consonant and add –er for the comparative
form; and double the consonant and add –est for the superlative form.
One-Syllable Adjective Ending with a Single Consonant with a Single Vowel before It
Comparative Form
Superlative Form
big
bigger
biggest
thin
thinner
thinnest
fat
fatter
fattest
My dog is biggerthan your dog.
My dog is the biggestof all the dogs in the neighborhood.
Max is thinnerthan John.
Of all the students in the class, Max is the thinnest.
My mother is fatterthan your mother.
Mary is the fattestperson I've ever seen.
Two-syllable adjectives.
With most two-syllable adjectives, you form the comparative with more and the superlative with most.
Two-Syllable Adjective
Comparative Form
Superlative Form
peaceful
more peaceful
most peaceful
pleasant
more pleasant
most pleasant
careful
more careful
most careful
thoughtful
more thoughtful
most thoughtful
This morning is more peacefulthan yesterday morning.
Max's house in the mountains is the most peacefulin the world.
Max is more carefulthan Mike.
Of all the taxi drivers, Jack is the most careful.
Jill is more thoughtfulthan your sister.
Mary is the most thoughtfulperson I've ever met.
If the two-syllable adjectives ends with –y, change the y to i and add –er for the comparative form. For the superlative form change the y to i and add –est.
Two-Syllable Adjective Ending with -y
Comparative Form
Superlative Form
happy
happier
happiest
angry
angrier
angriest
busy
busier
busiest
John is happier today than he was yesterday.
John is the happiest boy in the world.
Max is angrierthan Mary.
Of all of John's victims, Max is the angriest.
Mary is busierthan Max.
Mary is the busiestperson I've ever met.
Two-syllable adjectives ending in –er, -le, or –ow take –er and –est to form the comparative and superlative forms.
Two-Syllable Adjective Ending with -er, -le, or -ow
Comparative Form
Superlative Form
narrow
narrower
narrowest
gentle
gentler
gentlest
The roads in this town are narrowerthan the roads in the city.
This road is the narrowestof all the roads in California.
Big dogs are gentlerthan small dogs.
Of all the dogs in the world, English Mastiffs are the gentlest.
Adjectives with three or more syllables.
For adjectives with three syllables or more, you form the comparative with more and the superlative with most.
Adjective with Three or More Syllables
Comparative Form
Superlative Form
generous
more generous
most generous
important
more important
most important
intelligent
more intelligent
most intelligent
John is more generousthan Jack.
John is the most generousof all the people I know.
Health is more importantthan money.
Of all the people I know, Max is the most important.
Women are more intelligentthan men.
Mary is the most intelligentperson I've ever met.
Exceptions.
Irregular adjectives.
Irregular Adjective
Comparative Form
Superlative Form
good
better
best
bad
worse
worst
far
farther
farthest
little
less
least
many
more
most
Italian food is betterthan American food.
My dog is the best dog in the world.
My mother's cooking is worsethan your mother's cooking.
Of all the students in the class, Max is the worst.
Two-syllable adjectives that follow two rules. These adjectives can be used with -er and -est and with more and most.
Two-Syllable Adjective
Comparative Form
Superlative Form
clever
cleverer
cleverest
clever
more clever
most clever
gentle
gentler
gentlest
gentle
more gentle
most gentle
friendly
friendlier
friendliest
friendly
more friendly
most friendly
quiet
quieter
quietest
quiet
more quiet
most quiet
simple
simpler
simplest
simple
more simple
most simple
Big dogs are gentlerthan small dogs.
Of all the dogs in the world, English Mastiffs are the gentlest.
Big dogs are more gentlethan small dogs.
Of all the dogs in the world, English Mastiffs are the most gentle.