Could Jonah really have been swallowed by a great fish, survive for three days inside that creature and live to tell about it? Is this a myth, a parable, an allegory or real history?
The Bible, of course, does not speak of Jonah being swallowed by a "whale"; it specifically mentions a "great fish" (Jon 1:17). Some English versions of Matthew 12:40 use the word "whale," but the Greek original is ketos, a general word meaning a huge sea-monster. Taken as such, there are several sea-monsters that would be able to swallow a full-grown man easily enough, but the true whale, which has its home in the Arctic seas and is not found in the Mediterranean Sea, has a narrow throat that would generally prevent such a swallowing. There is another species of the same order in the Mediterranean Sea, however, which could swallow a man.
Ambrose John Wilson in the Princeton Theological Review for 1927 mentions a case of a sailor on a whaling ship near the Falkland Islands who was swallowed by a large sperm whale. The whale was later harpooned, and when it was opened up on deck the surprised crew found their lost shipmate unconscious inside its belly. Though bleached from the whale's gastric juices, he recovered, even though he never lost the deadly whiteness left on his face, neck and hands.
The problem with claiming that this text is a parable, allegory or myth is that each "solution" presents its own problems of literary genre. For example, parables are simple; they treat one subject. But the book of Jonah has at least two distinct parts: his flight and his preaching. Neither does Jonah fit the category of allegory, for there is no agreement on what the values are for each of the characters and events. The very diversity of answers is enough to state that allegory is not the solution. The same judgment would hold for suggesting that Jonah is a myth.
The book of Jonah, up until modern times, was everywhere treated as an historical record of the repentance of the city of Nineveh under the preaching of a man named Jonah. The apocryphal book Tobit has Tobit commanding his son Tobias to go to Media, for Tobit believes the word of God spoken about Nineveh. The Greek Septuagint text says that the preacher who predicted judgment on Nineveh was Jonah. In New Testament times, Jesus and the early believers took Jonah to be a real character. Thus, the objections to the book come down to this: it has too many miracles! But that is hardly an adequate basis on which to reject the internal claims of the book itself. Jonah is a believable account of a harrowing sea experience and of an unprecedented Gentile response to an ever-so-brief exposure to preaching about the need for repentance. But it happened!
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A. J. Wilson, "The Sign of the Prophet Jonah," Princeton Theological Review 25 (1927): 636. For more examples, see R. K. Harrison, Introduction of the Old Testament (Grand Rapids, Mich.: Eerdmans, 1969), pp. 907-8. See also the interesting article by G. Macloskie, "How to Test the Story of Jonah," Bibliotheca Sacra 72 (1915): 336-37, and, more recently, G. Ch. Aalders, The Problem of the Book of Jonah (London: Tyndale, 1948).