I have seen many times in English grammar books, 'If you had studied harder, you could have passed the test.' or 'If you studied harder, you could pass the test.'
But little have I seen the sentence, 'If you had studied harder, you could pass the test.'
Aside from English grammar, do you use this structure?
"If you had studied harder, you could have passed the test" implies that the test has taken place and the person failed.
"If you studied harder, you could pass the test" - the test hasn't happened yet, so they still have the chance to study.
Your version sounds odd because it mixes the tenses. I can imagine someone saying, shortly before the test, "If you had studied harder you would have a better chance of passing the test."
“If you had studied harder, you could pass the test” is quite unusual. I could imagine it being said just before you are taking the test. The person saying it tells you that you didn’t study hard enough, and therefore predicts you will fail the test.
