As a native speaker of English, these two sentences sound acceptable to me:
A full refund can be claimed if the school fails to provide a
textbook.A full refund could be claimed if the school failed to provide a
textbook.
But is it not the case that there are situations where both present and past tense cannot be used interchangeably when using "if' to create a conditional clause?
Best Answer
Could is the past tense of can as it is in may/might, will/would. Using a particular form (past or present) must be adhered to.