How much do you know about your dog? Have you heard his many different barks?
It may be that a dog barks because he is trying to copy the voice of people. Wild dogs never bark.
What a difference there is between a bark and a growl! When a dog barks, he holds his head up high. A bark is not a war cry. But when a dog growls, he lowers his head. A growl may mean he is ready to fight. The dog must guard his throat when he fights another animal.