Conditionals explain what happens if a condition is true or happens. They are built from two parts: the if-clause, which states the condition, and the main clause, which states the result. English uses different conditional patterns to show whether the condition is general, likely, unlikely, or impossible. Choosing the right pattern depends on time reference and how real the situation is.

A conditional sentence can start with the if-clause or the main clause. If the if-clause comes first, it is usually followed by a comma. If the main clause comes first, a comma is usually not used. The meaning stays the same; the order mainly affects emphasis and style.

Rule	Example
If-clause first uses a comma	If it rains, we will stay inside.
Main clause first usually has no comma	We will stay inside if it rains.
Either order is acceptable	If you call, I can help.

Use the zero conditional for general truths, scientific facts, and habits where the result always follows the condition. Both clauses use the present simple because the sentence describes a timeless relationship, not a specific future event. This conditional often sounds like a rule or instruction.

Rule	Example
Form: If + present simple, present simple	If you heat ice, it melts.
Use for facts and routines	If I drink coffee late, I sleep badly.
Also common for rules and instructions	If the light is red, you stop.

Use the first conditional for real and possible situations in the future and their likely results. The if-clause uses the present simple, and the main clause usually uses will plus the base verb. This pattern talks about a future consequence that depends on a condition that may happen.

Rule	Example
Form: If + present simple, will + base verb	If it rains, we will cancel the picnic.
Use for likely future outcomes	If you study, you will pass.
Main clause can use may or might for weaker certainty	If she calls, I might answer.

Use the second conditional for unreal or unlikely situations in the present or future. The if-clause uses the past simple, but it refers to the present or future, not the past. The main clause uses would plus the base verb to show the result is hypothetical. This conditional is common for imagining different realities and giving advice politely.

Rule	Example
Form: If + past simple, would + base verb	If I won the lottery, I would travel.
Past simple here signals unreality, not past time	If he had more time, he would exercise.
Use were for all subjects in formal style	If I were you, I would apologize.

Use the third conditional for unreal past situations: conditions that did not happen and results that did not happen. The if-clause uses past perfect, and the main clause uses would have plus the past participle. This conditional is common for regret, criticism, and imagining alternative past outcomes.

Rule	Example
Form: If + past perfect, would have + past participle	If we had left earlier, we would have arrived on time.
Use to express regret or missed opportunities	If I had studied, I would have passed.
Use for past criticism and evaluation	If you had listened, you would have understood.

Mixed conditionals combine different time references in the condition and the result. A common pattern is a past condition with a present result, showing that something in the past still affects the present. Another pattern is a present condition with a past result, showing an ongoing state causing a past outcome. The tense choice reflects the time of each clause, not a fixed conditional type.

Rule	Example
Past condition, present result: If + past perfect, would + base verb	If I had taken the job, I would live in London now.
Present condition, past result: If + past simple, would have + past participle	If she were more careful, she would have avoided the mistake.

The result clause does not always use will or would. Modals change meaning: can for ability, may or might for possibility, should for advice, and must for strong necessity. You can also use an imperative in the main clause to give instructions. The if-clause tense still follows the conditional type, while the modal shows attitude and strength.

Rule	Example
can for ability or permission	If you finish early, you can leave.
may or might for possibility	If he calls, I might be busy.
should for advice	If you feel sick, you should rest.
Imperative for instructions	If you see Anna, tell her to call me.

Unless means if not and introduces the only condition that prevents the result. It is used in place of an if-clause with a negative meaning, but you usually keep the verb positive after unless. It commonly appears in rules, warnings, and agreements. The tense in the unless-clause follows the same logic as an if-clause.

Rule	Example
Unless = if not	You will fail unless you study.
Usually avoid double negatives with unless	I will go unless it rains.
Common in warnings and conditions	Unless you pay today, we will cancel the order.

English often uses alternatives to if to express conditions with different meanings and levels of formality. Provided that and as long as emphasize a strict requirement. In case means as preparation for a possible problem. Even if means the result is true despite the condition. These forms help you express precise conditional relationships beyond basic if.

Rule	Example
provided that or providing that for strict conditions	You can borrow my car provided that you drive carefully.
as long as for requirements or limits	I will help as long as you are honest.
in case for precaution	Take a jacket in case it gets cold.
even if for contrast	Even if it rains, we will go.

Choosing a conditional is mainly about reality and time. Zero conditional states general cause and effect. First conditional predicts a likely future result. Second conditional imagines an unreal or unlikely present or future. Third conditional imagines a different past. Mixed conditionals link different times to show lasting consequences or background causes.