In what circumstances will a defendant be allowed to amend his pleadings?

In Marin v. Rask, 2000 ABQB 931 at para. 14, 282 A.R. 308, Veit J. delineated the four exceptions in which the general rule allowing amendments to pleadings does not apply: [T]here is no amendment where it would create serious prejudice which payment of costs could not repair; there is no amendment where the amendment would be hopeless; there is no amendment where the amendment would add a new cause of action outside the limitation period for suing; there is no amendment where the failure to plead earlier, or the amendment itself, involves bad faith.