Your dad is putting the cart before the horse.
First, ask him to prove the existence of an absolute moral standard, and then have him prove that it must come from a moral lawgiver. By trying to answer his question in such a manner, you are allowing him to take conclusions he needs to prove as a given.
Every single person I have ever seen appeal to an absolute moral standard is making an appeal to emotion in the hopes that no one will question them about its existence.
First, ask him to prove the existence of an absolute moral standard, and then have him prove that it must come from a moral lawgiver. By trying to answer his question in such a manner, you are allowing him to take conclusions he needs to prove as a given.
Every single person I have ever seen appeal to an absolute moral standard is making an appeal to emotion in the hopes that no one will question them about its existence.
Even if the open windows of science at first make us shiver after the cozy indoor warmth of traditional humanizing myths, in the end the fresh air brings vigor, and the great spaces have a splendor of their own - Bertrand Russell
