1. Lesson Overview
In this lesson, you will study the zero conditional, which is used to express general truths, scientific facts, and situations that are always true under certain conditions.
The zero conditional describes situations in which the condition and the result occur regularly or inevitably.
Example:
If water reaches 100°C, it boils.
This sentence expresses a scientific fact, not a specific future possibility.
The zero conditional therefore describes universal relationships between conditions and results.
By the end of this lesson, you will be able to:
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understand how the zero conditional expresses general truths
-
apply the structure if + present simple, present simple
-
recognise common signal expressions used in zero conditional sentences
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identify and correct common errors involving zero conditional structures
2. Concept Introduction
Consider the following sentence.
If the temperature drops below 0°C, water freezes.
This sentence expresses a general rule.
| Clause Type | Example |
|---|---|
| condition | If the temperature drops below 0°C |
| result | water freezes |
Both clauses use the present simple tense because the sentence describes something that is always true.
3. Core Explanation
The zero conditional is used to describe situations that always happen when a specific condition occurs.
These situations may include:
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scientific facts
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natural laws
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general truths
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routine outcomes
Example:
If metals are heated, they expand.
The sentence does not describe a future event. Instead, it explains a universal physical principle.
Basic Structure
Zero conditional sentences follow a simple structure:
If + present simple, present simple
Example:
If people exercise regularly, they improve their health.
Clause Order
The order of clauses may change.
If-clause first
If the pressure increases, the volume decreases.
Result clause first
The volume decreases if the pressure increases.
4. Rule Table
Zero Conditional Structure
| Structure | Example |
|---|---|
| If + present simple, present simple | If water freezes, it expands. |
| Present simple + if + present simple | Water freezes if the temperature drops below 0°C. |
Common Verbs Used in Scientific Statements
| Verb | Example |
|---|---|
| boil | Water boils at 100°C. |
| freeze | Water freezes below 0°C. |
| expand | Metals expand when heated. |
| dissolve | Salt dissolves in water. |
These verbs commonly appear in zero conditional statements describing scientific facts.
5. Usage
1. Expressing scientific facts
Example:
If water reaches 100°C, it boils.
2. Describing natural laws
Example:
If gravity is removed, objects float.
3. Explaining cause-and-effect relationships
Example:
If pressure increases, the temperature rises.
4. Describing general behaviour
Example:
If people sleep well, they feel more energetic.
5. Describing regular outcomes
Example:
If the system overheats, it shuts down automatically.
6. Signal Words
Several expressions commonly introduce zero conditional situations.
| Signal Expression | Example |
|---|---|
| if | If water freezes, it expands. |
| when | When water freezes, it expands. |
| whenever | Whenever the temperature drops, ice forms. |
| every time | Every time the system restarts, the settings reset. |
In many cases, when and whenever may replace if when the result is certain.
Example:
When water freezes, it expands.
7. Special Cases
Using “When” Instead of “If”
Because the zero conditional describes facts, the word when is often used instead of if.
Example:
When metals are heated, they expand.
This emphasises that the result always occurs.
Imperatives in Zero Conditional
Sometimes the result clause may contain an imperative (instruction).
Example:
If the alarm sounds, leave the building immediately.
This structure is common in instructions and safety procedures.
8. Additional Notes
Zero conditional sentences are common in:
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scientific writing
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technical explanations
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instructions
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rules and regulations
Example:
If the machine overheats, switch it off immediately.
Such sentences explain predictable cause-and-effect relationships.
9. Common Errors
⚠ Using future tense in the if-clause
Incorrect:
If water will reach 100°C, it boils.
Correct:
If water reaches 100°C, it boils.
Explanation:
Zero conditional clauses use present simple, not future forms.
⚠ Using different tenses incorrectly
Incorrect:
If water reaches 100°C, it will boil.
Correct:
If water reaches 100°C, it boils.
Explanation:
Zero conditional uses present simple in both clauses.
⚠ Incorrect word order
Incorrect:
If freezes water, it expands.
Correct:
If water freezes, it expands.
Explanation:
The subject must appear before the verb.
⚠ Missing subject
Incorrect:
If reach 100°C, water boils.
Correct:
If water reaches 100°C, it boils.
Explanation:
Both clauses must contain a complete subject–verb structure.
⚠ Incorrect punctuation
Incorrect:
If water freezes it expands.
Correct:
If water freezes, it expands.
Explanation:
A comma usually separates the clauses when the if-clause comes first.
10. Lesson Mastery
After completing this lesson, you should now be able to:
✅ understand how the zero conditional expresses general truths
✅ use the structure if + present simple, present simple correctly
✅ recognise common signal expressions used in zero conditional sentences
✅ identify and correct errors involving zero conditional structures