Conditional tenses are used to speculate about what could happen, what
might have happened, and what we wish would happen. In English, most
sentences using the conditional contain the word
if. Many
conditional forms in English are used in sentences that include verbs in
one of the past tenses. This usage is referred to as "
the unreal past"
because we use a past tense but we are not actually referring to
something that happened in the past. There are five main ways of
constructing conditional sentences in English. In all cases, these
sentences are made up of an
if clause and a main clause. In many negative conditional sentences, there is an equivalent sentence construction using "unless"
instead of "if".
| Conditional sentence type |
Usage |
If clause verb tense |
Main clause verb tense |
|---|
| Zero |
General truths |
Simple present |
Simple present |
| Type 1 |
A possible condition and its probable result |
Simple present |
Simple future |
| Type 2 |
A hypothetical condition and its probable result |
Simple past |
Present conditional or Present continuous conditional |
| Type 3 |
An unreal past condition and its probable result in the past |
Past perfect |
Perfect conditional |
| Mixed type |
An unreal past condition and its probable result in the present |
Past perfect |
Present contditional |
The zero conditional
The zero conditional is used for when the time being referred to is
now or always and the situation is
real and possible.
The zero conditional is often used to refer to general truths. The
tense in both parts of the sentence is the simple present. In zero
conditional sentences, the word "if" can usually be replaced by the word
"when" without changing the meaning.
| If clause |
Main clause |
|---|
| If + simple present |
simple present |
| If this thing happens |
that thing happens. |
| If you heat ice |
it melts. |
| If it rains |
the grass gets wet. |
Type 1 conditional
The type 1 conditional is used to refer to the
present or future where the
situation is real.
The type 1 conditional refers to a possible condition and its probable
result. In these sentences the if clause is in the simple present, and
the main clause is in the simple future.
| If clause |
Main clause |
|---|
| If + simple present |
simple future |
| If this thing happens |
that thing will happen. |
| If you don't hurry |
you will miss the train. |
| If it rains today |
you will get wet. |
Type 2 conditional
The type 2 conditional is used to refer to a time that is
now or any time, and a situation that is
unreal.
These sentences are not based on fact. The type 2 conditional is used
to refer to a hypothetical condition and its probable result. In type 2
conditional sentences, the if clause uses the simple past, and the main
clause uses the present conditional.
| If clause |
Main clause |
|---|
| If + simple past |
present conditional or present continuous conditional |
| If this thing happened |
that thing would happen. (but I'm not sure this thing will happen) OR
that thing would be happening. |
| If you went to bed earlier |
you would not be so tired. |
| If it rained |
you would get wet. |
| If I spoke Italian |
I would be working in Italy. |
Type 3 conditional
The type 3 conditional is used to refer to a time that is
in the past, and a situation that is
contrary to reality.
The facts they are based on are the opposite of what is expressed. The
type 3 conditional is used to refer to an unreal past condition and its
probable past result. In type 3 conditional sentences, the if clause
uses the past perfect, and the main clause uses the perfect conditional.
| If clause |
Main clause |
|---|
| If + past perfect |
perfect conditional or perfect continuous conditional |
| If this thing had happened |
that thing would have happened. (but neither of those things really happened) OR
that thing would have been happening. |
| If you had studied harder |
you would have passed the exam. |
| If it had rained |
you would have gotten wet. |
| If I had accepted that promotion |
I would have been working in Milan. |
Mixed type conditional
The mixed type conditional is used to refer to a time that is
in the past, and a situation that is
ongoing into the present.
The facts they are based on are the opposite of what is expressed. The
mixed type conditional is used to refer to an unreal past condition and
its probable result in the present. In mixed type conditional sentences,
the if clause uses the past perfect, and the main clause uses the
present conditional.
| If clause |
Main clause |
|---|
| If + past perfect or simple past |
present conditional or perfect conditional |
| If this thing had happened |
that thing would happen. (but this thing didn't happen so that thing isn't happening) |
| If I had worked harder at school |
I would have a better job now. |
| If we had looked at the map |
we wouldn't be lost. |
| If you weren't afraid of spiders |
you would have picked it up and put it outside. |
SOURCE :
http://www.edufind.com/english-grammar/conditional/
http://grammar.ccc.commnet.edu/grammar/conditional2.htm
http://www.englisch-hilfen.de/en/grammar/if.htm
