In case and Unless

In case

'In case' is used to express the possibility of something happening. It is used to express the idea of doing something to avoid a problem later on. It can also give a reason for an action.

I'll take an umbrella in case it rains. (there is a possibility that it will rain – it is not raining now – I think it is a good idea to take an umbrella)
Notice that the verb after 'in case' is in a present tense even though the time is a future time. Present tenses are used with 'in case' to express a 'possible future'

In case + of

'In case + of' means 'if there is'
In case of emergency, call this number. (If there is an emergency, call this number.)

Unless

Unless means 'except if' or 'only if'. Unless replaces 'if + a negative verb':
Sarah won't come unless you invite Peter.
Sarah will only come if you invite Peter.
Sarah won't come if you don’t invite Peter.

We'll spend the day at the park unless it rains.
If it doesn’t rain we'll spend the day at the park.
If it rains, we won't spend the day at the park.

Lesson by Tristan, teacher at EC Malta English school

Now use either 'in case' or 'unless' in the following:

• 1. Peter won’t call you _ you ask him to.
  
  in case
  unless
  
  
• 2. Take the spare key _ I am still out when you get back.
  
  in case
  unless
  
  
• 3. Don’t forget to keep the receipt _ you need it later.
  
  unless
  in case
  
  
• 4. _ a fire do not use the lifts.
  
  Unless
  In case of
  
  
• 5. Maria won’t speak to you _ you apologise for what you did.
  
  unless
  in case
  
  
• 6. The batteries won’t last long _ you charge them properly.
  
  unless
  in case
  
  
• 7. Here’s a number you can call _ an emergency.
  
  unless
  in case of
  
  
• 8. Take your driving license _ you need to rent a car.
  
  unless
  in case