Hi Mkyol
After "I wish", you use the past perfect form of the verb to refer to the unreal past -- like what you find in a type 3 conditional sentence.
- I wish I had studied harder for my exam. = I did not study very hard for my exam. (If I had studied harder for my exam, I would have passed.)
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After "I wish", we use the past form of the verb to refer to an unreal or hypothetical present -- similar to a type 2 conditional sentence. For example:
- I wish I had a car. = I do not have a car. (It would be wonderful if I had a car.)