Impossible – It can never happen. Only a few things can be impossible, things might stop being impossible when technology develops. Some things will never stop being impossible even with technology eg. Akshay being able to walk through Joel.
Very unlikely – There’s not much of a chance that it will happen. It might only happen once a year or if you are not sure if it could happen.
Even chance – There is a 50% chance that this might happen. It could change easily. It could happen and it could not.
Likely – it can happen but not always. You have more chance of it happening than not.
Certain – It will definitely happen no matter how cold it is or what the weather is. It is going to happen for sure.