I have a question about how to explain when to use the -al, for example economic vs economical and historic vs historical. Both can be used as adjectives, correct? But what else? Thank you!
historic=important in history
economic=related to economy
historical=related to history
"I have a question about how to explain when to use the -al,"
Your question rightfully turnes up looking at the examples.
My answer is "I do not know."