Over at JesusCreed, contributor RJS lays out the arguments for both common interpretations of the book of Jonah.
I’ve long thought the greatest stumbling block to interpreting Jonah as literal history is not the great fish but rather the repentance of the Ninevites—an event of which extrabiblical records know nothing and, on the contrary, eighth-century Assyrian history would seem to emphatically refute.
Have a look at what RJS has to say, however, and make up your own minds.