When are conditional sentences (if-clauses) used?

In the following chart, you will find a juxtaposition of how to use the if-clauses (full conditional sentences), which makes it easier for you to choose the appropriate type. Decide according to this principle:

		Can the condition be fulfilled? Can the result occur?
Yes, condition can be fulfilled; result can occur. (→ probable)		Yes, condition could be fulfilled; result could occur. (→ rather unlikely)		No, condition can no longer be fulfilled; result can no longer occur. (→ impossible)
if-clause type I (1st conditional)		if-clause type II (2nd conditional)		if-clause type III (3rd conditional)
“If I leave, I will catch the train.”		“If I left, I would catch the train.”		“If I had left, I would have caught the train.”
↙ ↘		↙ ↘		↙ ↘
if-clause	Main clause	if-clause	Main clause	if-clause	Main clause
present	future (will)	past	present conditional	past perfect	past conditional
‘leave’	‘will catch’	‘left’	‘would catch’	‘had left’	‘would have caught’

Further explanations related to the ‘Comparison of if-clauses’

The following explanations refer to the topic ‘Juxtaposition of the if-sentences (conditional sentences) in English’ and could help you too:

• Using the zero conditional sentence
• Word order / syntax in if-sentences
• List of exercises about if-sentences