Understanding Conditionals
Learn how a conditional sentence is built from two connected parts, and how the different conditional patterns relate to one another.
The building blocks of a conditional
A conditional sentence is built from two connected parts.
A conditional sentence is made of two clauses. The if-clause states a condition, usually introduced by if or a related word. The main clause states the result that depends on that condition.
In the sentence If it rains, we will stay inside., if it rains is the if-clause, and we will stay inside is the main clause.
The verb form used in each clause signals how real, likely or hypothetical the condition is meant to sound. This is what separates the different conditional patterns from one another, each covered in its own lesson.
Before you begin
Understanding conditionals is the starting point for the topic.
This lesson explains how conditional sentences are built. For an overview of the topic as a whole, including links to every individual pattern, begin with the Conditionals page.
The two clauses
Every conditional sentence has an if-clause and a main clause.
Compare the two parts of a conditional sentence.
01
The If-Clause
States the condition, introduced by if or a related word.
If it rains,
02
The Main Clause
States the result that depends on the condition.
we will stay inside.
The if-clause can appear first or second in the sentence.
Either clause can come first without changing the meaning of the sentence. What changes is the punctuation used between them.
Word order and punctuation
The if-clause can come first or second, but punctuation changes.
If-clause first: use a comma
If it rains, we will stay inside.
If-clause second: no comma
We will stay inside if it rains.
Both orders are correct and mean the same thing.
How real is the condition?
English matches a verb pattern to how real the condition sounds.
This is the idea behind the four core conditional patterns, each covered in its own lesson.
A general fact uses the zero conditional.
If you heat water to 100 degrees, it boils.
A realistic future possibility uses the first conditional.
If it rains, we will stay inside.
An unlikely or imaginary present situation uses the second conditional.
If I won the lottery, I would travel the world.
An impossible past situation uses the third conditional.
If I had known earlier, I would have helped.
Some sentences combine two different time periods.
If I had studied medicine, I would be a doctor now.
Beyond “if”
Other words can introduce a condition too.
Several related words and phrases work alongside, or in place of, if, each covered in its own lesson.
Provided, providing and as long as state a required condition.
You can go, provided you finish your homework first.
Wish and if only express a wish about something not true.
I wish I had more time this week.
Identifying the two clauses
Ask which clause states the condition, and which states the result.
Use these steps to find the two clauses in a conditional sentence.
01
Look for if, unless, in case or a similar linking word.
This word usually introduces the clause that states the condition.
02
Find the clause that states what needs to happen.
This is the if-clause, whether it comes first or second in the sentence.
03
Find the clause that states what follows the condition.
This is the main clause, describing the result.
04
Check the verb forms used in both clauses.
The verb pattern signals which conditional type the sentence belongs to.
Common mistakes
Do not confuse the if-clause with the main clause.
Assuming the first clause is always the condition.
We will stay inside if it rains.
Here, the main clause comes first, and the if-clause comes second.
The if-clause is the clause introduced by if or a similar word, wherever it appears in the sentence.
Forgetting the comma when the if-clause comes first.
Not: If it rains we will stay inside.
Correct: If it rains, we will stay inside.
Adding a comma when the if-clause comes second.
Not: We will stay inside, if it rains.
Correct: We will stay inside if it rains.
Check your understanding
Can you identify the parts of a conditional sentence?
Choose the correct answer for each question.
In “If it rains, we will stay inside,” which part is the if-clause?
✅ Exactly! The if-clause is the part that states the condition.
❎ Not quite. Look for the clause introduced by if.
The if-clause states what needs to happen; the main clause states what follows.
Does “We will stay inside if it rains” need a comma before “if”?
✅ Exactly! A comma is only needed when the if-clause comes first.
❎ Not quite. Check whether the if-clause comes before or after the main clause here.
In “Unless you hurry, you will miss the bus,” which word introduces the condition?
✅ Exactly! Unless introduces the clause that states the condition.
❎ Not quite. Look for the word that plays the same role as if here.
In “Take an umbrella in case it rains,” which clause states the result?
✅ Exactly! “Take an umbrella” is the main clause, stating what to do.
❎ Not quite. Look for the clause that states the precaution being taken, not the reason for it.
Choose the best explanation
Select the sentence that explains the structure correctly.
Why does “If it rains, we will stay inside” need a comma, while “We will stay inside if it rains” does not?
✅ Exactly! The comma marks the end of the if-clause, but only when it comes before the main clause.
❎ Not quite. Compare the position of the if-clause in each sentence.
Why can “unless” replace “if…not” in a conditional sentence?
✅ Exactly! “Unless” states a negative condition on its own, without a separate “not.”
❎ Not quite. Think about what “unless” already means by itself.
Why does the verb pattern in a conditional sentence matter?
✅ Exactly! This is what distinguishes the zero, first, second and third conditionals from one another.
❎ Not quite. Think about what changes between “If it rains, we will stay inside” and “If I won the lottery, I would travel the world.”
Try it another way
Complete each sentence with the correct word.
Type the word that belongs in each blank.
✅ Exactly! Unless means “if not.”
❎ Not quite. Think of the word that replaces “if…not.”
✅ Exactly! In case describes a precaution taken for something that might happen.
❎ Not quite. Think of the phrase used for taking a precaution.
✅ Exactly! Provided states a condition that must be met.
❎ Not quite. Think of the word often used for permission or agreement.
Edit the sentence
Rewrite each sentence with the correct structure.
Use the note in brackets to decide what needs to change.
If it rains we will stay inside. (add the missing comma)
✅ Exactly! A comma follows the if-clause when it comes first.
❎ Not quite. Add a comma after the if-clause.
We will stay inside, if it rains. (remove the unnecessary comma)
✅ Exactly! No comma is needed when the if-clause comes second.
❎ Not quite. Remove the comma before “if.”
If you don’t hurry, you will miss the bus. (rewrite using unless)
✅ Exactly! Unless replaces if…not.
❎ Not quite. Replace “if you don’t” with “unless you.”
Quick review
A conditional sentence always connects a condition with a result.
A conditional sentence connects a condition with a result.
The if-clause states the condition; the main clause states the result.
An if-clause first needs a comma; an if-clause second does not.
The zero, first, second and third conditionals move from general facts, to realistic possibilities, to imaginary situations, to alternate versions of the past.
Mixed conditionals combine two of these time periods in one sentence.
Words such as unless, in case, provided, providing, as long as, wish and if only introduce or relate to a condition in other ways.
Remember
Look for the two clauses first, then check the verb pattern.
Once the if-clause and the main clause are identified, the verb forms used in each one point to which conditional pattern is being used. That structure stays the same across every pattern covered in the lessons that follow.