Every day you talk about what happens when something else happens. 'If you press this button, the machine starts.' 'If the bus is late, I walk.' You also make real plans for the future: 'If it is sunny on Saturday, we will have a picnic.' These are conditional sentences, and you cannot get through a normal day of English without them.

If you use the wrong tense in these sentences, people may still understand you, but your English will sound wrong every single time, because conditionals are so common. Worse, sometimes the meaning changes. Learning two simple patterns — the zero conditional for facts and the first conditional for real future plans — fixes hundreds of sentences at once.

A conditional sentence has two parts. The 'if-clause' gives the condition: 'If it rains...'. The result clause gives what happens: '...the ground gets wet.' You can put the if-clause first or second. 'If you heat ice, it melts' and 'Ice melts if you heat it' mean the same thing. When the if-clause comes first, put a comma after it. When it comes second, you do not need a comma.

The zero conditional is for things that are always true: facts, habits, and rules. The form is simple: if + present simple, then present simple again. 'If I drink coffee at night, I sleep badly.' 'If the shop closes early, we go somewhere else.' Both parts use the present tense because the sentence is not about one future moment — it is about every time.

The first conditional is for one real possibility in the future. The form is: if + present simple, then will + base verb. 'If it snows tonight, the school will close.' 'If you call me later, I will answer.' Notice something strange but very important: the if-clause talks about the future, but it uses the PRESENT tense. English does this on purpose. The word 'if' already tells us we are talking about a possible future, so we do not add 'will' inside the if-clause.

Compare the two patterns. Zero: 'If I eat fish, I get sick.' This is always true for me — a fact about my body. First: 'If I eat this fish, I will get sick.' This is about one plate of fish, one future moment. The if-clause looks the same in both; the difference is in the result clause: present simple for always-true, 'will' for one future result.

You can also use the first conditional to give warnings, promises, and offers. 'If you touch that pan, you will burn your hand' is a warning. 'If you help me move, I will buy you dinner' is a promise. In the result clause you can use other words instead of 'will', such as 'can', 'might', or an imperative: 'If you feel tired, take a break.'

1. 1. If you mix blue and yellow, you get green.

   Zero conditional: a fact that is true every time, so both parts use the present simple.

2. 2. If I skip breakfast, I feel weak by noon.

   Zero conditional for a personal habit — 'feel', not 'will feel'.

3. 3. Water boils if you heat it to one hundred degrees.

   The if-clause can come second; then you do not need a comma.

4. 4. If the printer stops, turn it off and on again.

   A rule at work: the result clause can be an instruction (imperative).

5. 5. If the train is full, we usually wait for the next one.

   Zero conditional describing what normally happens, again and again.

6. 6. If it snows tonight, the flight will be late.

   First conditional: one real future possibility, so the result uses 'will'.

7. 7. I will call you if I finish work early.

   'Finish', not 'will finish' — no 'will' inside the if-clause.

8. 8. If you order now, the shop will deliver it tomorrow.

   A first conditional promise, common in shopping situations.

9. 9. Will you come to the party if I invite your sister too?

   A first conditional question: 'will' moves in front of 'you'.

10. 10. If she doesn't rest, she will get worse.

    A health warning: the if-clause can be negative with 'doesn't'.

11. 11. We won't go hiking if the weather stays bad.

    The result clause can be negative: 'won't go'.

12. 12. If you feel dizzy, sit down and drink some water.

    Health advice with an imperative result — no 'will' needed.

13. 13. If my friends visit, I will cook something special.

    'Visit' is present simple even though the visit is in the future.

14. 14. You might miss the bus if you leave after eight.

    You can use 'might' instead of 'will' when you are less sure.

15. 15. If the hotel has a pool, the kids will be happy.

    Travel context: present simple 'has' in the if-clause, 'will be' in the result.

The biggest mistake is putting 'will' inside the if-clause. Learners say 'If it will rain tomorrow, we will stay home.' The correct sentence is 'If it rains tomorrow, we will stay home.' In English, 'if' plus the present tense already points to the future. Adding 'will' after 'if' is double marking, and native speakers never do it in this kind of sentence. Remember: the future lives in the result clause, not in the if-clause.

A second mistake is mixing up the zero and first conditionals. 'If I drink coffee, I will not sleep' sounds like one special night. If you mean it is always true for you, say 'If I drink coffee, I don't sleep.' Ask yourself: am I talking about every time (zero, present + present) or about one future situation (first, present + will)?

A third mistake is forgetting the third-person -s in the if-clause. Learners write 'If she arrive late, we will start without her.' Because the if-clause uses the normal present simple, all the normal rules apply: 'If she arrives late, we will start without her.'

• Never put 'will' right after 'if' in these sentences.
• Always true? Use present + present: 'If you heat ice, it melts.'
• One real future case? Use present + will: 'If it rains, we will stay in.'
• If-clause first: add a comma. If-clause second: no comma.
• The result clause can also use 'can', 'might', or an instruction.
• The if-clause follows normal present simple rules, including third-person -s.