What
is the difference between the use of when and if in
all types of conditional sentences?
Trung
from Vietnam writes:
Would
you please explain to me the differences in use between incase and if?
Roger
Woodham replies:
When
or if?
We use when for things that are certain to happen
in the future:
I'll buy you a pair of gloves when I go shopping this
afternoon.
I'll give you a ring when I get home from school.
Note that although the reference is clearly to the future, we use
the present tense in the when-clause.
We use if for things that may happen and which we are not
certain about:
If I decide to come to London this year, I'll come
and visit you.
I'm going to call the police if she's not back within
the hour.
If you make the salads, I'll prepare the barbecue.
In all of these examples, we are talking about future conditions
and whether we use when or if depends upon the certainty
of things happening.
However, when and if are interchangeable when
we are talking about general conditions that always apply when if
means almost the same as whenever. Compare the following:
I keep the air-conditioning on at night if the temperature
goes above 30 degrees.
I keep the air-conditioning on at night whenever / when
the temperature goes above 30 degrees.
If the green flag is flying, it's quite safe to swim
here
You can swim here whenever / when / provided the green
flag is flying.
In
case
We use in case to talk about taking precautions,
doing something because something else might happen:
During the drought, keep the bath filled with water - just
in case it is needed.
I've bought some candles in case there are more electricity
cuts.
In case I forget, remind me to check the tyre pressure
before we load up the car.
In case or if?
When we use in case we are mostly describing future possible
situations. When we use if we are talking about conditions
that apply. Compare the following and note the differences
in meaning.
I'll fill up the car with petrol in case you need to go
to Brighton. ( = I'll fill up now, because you might need
it later.)
I'll fill up the car with petrol if you need to go to
Brighton. ( = Let me know if you need to go to Brighton and
then I'll fill up with petrol.)
Take the mobile phone with you in case the car breaks
down.
If the car breaks down, give me a ring.
in case of
Note that in case of is a prepositional phrase used with
a noun which is similar in meaning to an if-clause.
Compare the following:
In case of fire, exit from the building by the stairs.
Do not attempt to use the lift.
If there is a fire, leave the building via the stairs.
Don't try to use the lift.
In cases of difficulty, phone this help line. If you experience any problems, phone this help line.
If
you would like more practice more please visit our in the You, Meand Us part of our
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