'If' and 'Unless' - Zero (0) and First 'Conditionals' - as they are often known.

The 'Zero' (0) or 'Present Condition' or 'Conditional': it's easy!
n.b. if = when, for example, when you are talking about something which is always true on all occasions.
e.g. 'if/when you boil water, it turns to steam'.
n.b. Use the Present Simple Tense in both clauses.
e.g. When I'm ill, I go to bed.
or If I'm ill, I go to bed.
In this case the above two sentences mean the same thing.

'if' tells you there is a condition! Careful! You can say 'When the sun rises we'll get up' but you can't say 'If the sun rises, we'll get up'! The sun always rises!

The First 'Conditional': there are 2 clauses - in one: there is a potential condition which exists, which begins with 'if' - then if this condition is true then the 'main' statement is true.
e.g.  Potential condition + Main statement = If the car breaks down + we will have a problem!'

If you say this, it means there is a future possibility and probably quite a strong one!

Practice Exercise:

Choose whether to use the 'Factual Condition' (The (0) Condition) - or the 'First Conditional', (or the 'will-condition'), the 'likely' condition, in the examples below. The answers will give you alternatives in case you want to experiment and you want to know if you are right or not!

1. If I…..in the country, the car…….dirty because it's very muddy. (drive, get)
2. If ice………it……….water. (melt, become/or turn into).
3. If you………..a tin of cat food, the cat…….(open,come).
4. Unless we……..the house, the neighbours …….we're pigs. (clean, think)
5. If you …..garlic, your breath…….(eat, smell)
6. Unless you……….smoking, you ………..bronchitis. (give up, get)
7. If you……….carefully, you……..an accident. (not drive, have)
8. If you……water the plants, they…… (not water, no survive)
9. if the weather ……..warmer, we….all…..to death. (not get, freeze).
10. If the Prime Minister………a bodyguard, she…..in danger. (not have, be).
11. If you …….cheese, you…………cheesecake. (not like, not like)
12. Unless you……..the plants, they………… (water, die).

Answers:
1. If I drive in the country, the car gets dirty. Or this could also be the 'will' condition e.g. the car will get dirty.
2. If ice melts, it turns into water. (Fact).
3. If you open a tin of cat food the cat comes running. (Fact, but also could be 'will' condition for warning).
4. Unless we clean the house, the neighbours think…..(Fact)!
5. If you eat garlic, your breath smells. (Fact).
6. Unless you give up smoking, you will get bronchitis. This is not a fact, it is likely. This functions as a warning.
7. If you don't drive carefully, you will have an accident. (same as 6 above).
8. If you don't water the plants, they won't survive. (notice 'the plants', so this is a specific case, so it's 'will not' or 'won't'. If you just say 'plants', meaning all plants, then it's a fact and you can use the Present Simple form in both parts e.g. If you don't water plants, they don't survive).
9. If the weather doesn't get warmer we will all freeze to death. (Could be either).
10. If the P.M. doesn't have a bodyguard she will be in danger.
11. If you don't like cheese, you won't like cheesecake. (could be either)
12. Unless you water the plants they will die. (This is the converse of 8 above).

See The A -Z of English Grammar & Usage for the rules.

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