First I will give a few of the best arguments for Jonah not being literal, and then I will explain why Jonah should be read as a literal history.
Arguments for Jonah not being literal
For me, the most compelling argument as to why someone would view Jonah as a work of fiction is that the literary devices in the book, such as irony and poetic justice, are almost too perfect. Everything that happens in the story is so extreme, that one could be tempted to believe that it did not actually happen in real life. For example, Jonah is fast asleep while the ship is going through an intense storm that is on the verge of tearing the ship apart. The heathen sailors are rebuking the man of God for not praying. The heathen sailors are all converted to worshiping the LORD. Later, the men of Nineveh convert to worshiping the LORD en masse. All of these plot points are so extreme that I can see why someone might think that this is a parable using radical situations to drive home a spiritual truth, as opposed to documenting events that actually happened.
Another somewhat compelling argument is that there seems to be a lack of historical context in the sense that we are not given the names of any kings who are reigning. There is nothing in the book itself to tell us when these events happened, other than the identity of Jonah himself, whom we can place in a historical context based on 2 Kings 14:25. The book immediately jumps into the action in Jonah 1:1 and ends abruptly in Jonah 4:11. Other narrative books tend to give more historical context either at the beginning or end of the book, or in both places.
Arguments for Jonah being literal
The Bible contains many genres, but some genres are more common than others. There are large sections of the Old Testament that are clearly historical narratives, whereas there are relatively few allegories and parables. Therefore, it stands to reason that we would start with the assumption that Jonah is yet another historical narrative, and that we would not regard it as fictional without a very compelling reason.[1]
Some would point to a late composition date as a reason to regard the book of Jonah as fictional, but this argument is flawed for a couple reasons. First, we cannot be sure that Jonah was composed at a late date. The book's use of the word טעם is considered an Aramaism,[2] but this is not necessarily indicative of late composition. The action is taking place in a foreign country, so the use of a somewhat exotic word is not too surprising. Second, even if the book were composed many centuries after the events it records, this does not mean it is not recording real events. Many historical narratives in the Old Testament were written centuries after the fact. Scripture is inspired by God, and therefore it does not rely on human memory or eyewitnesses alone to get the story right.
Another objection to the historicity of Jonah is that it seems far-fetched that the capital of the Assyrian empire would have such dramatic repentance, and that there would be no historical record of it. First, the vast majority of historical records from antiquity have not survived, so absence of evidence is not evidence of absence. Second, the book of Jonah never refers to Nineveh as the capital of the Assyrian empire, and it never refers to Nineveh's king as the king of Assyria.[3] In fact, if we use 2 Kings 14:25 to place the book of Jonah in its proper historical context, we find that Nineveh was decidedly not the capital of the Assyrian empire at this time.[4] Therefore, we can conclude that the king of Nineveh was the king of the city of Nineveh alone, which is the only claim being made by the Bible. It is thus one city that repented at the preaching of Nineveh, and the historical record of this event is the book of Jonah itself. Nothing else regarding this incident has survived.
A good reason not to regard Jonah as a parable is the length of the book. Parables tend to be much shorter than the book of Jonah. Parables in both the Old and New Testaments tend to be a few verses long.[5] Even a long parable, like the story of the prodigal son, is only 22 verses long. The book of Jonah on the other hand is 48 verses long, which is substantially longer than the longest of biblical parables. Also, the book of Jonah consists of four distinct chapters, which makes it too long and complex to fit the genre of being parable. Furthermore, parables do not use names. A parable would speak of "a certain prophet" not "Jonah the son of Amittai."
Parables tend to tell stories about things that happen, or at least could happen, in everyday life.[6] I have often heard a parable defined as "an earthly story with a heavenly meaning." The book of Jonah, on the other hand, is far from describing ordinary life. It is packed with miracles and supernatural occurrences. Thus, it is ironic that scholars would point to the extraordinary occurrences in the book of Jonah as evidence that it is parable, when in reality, those are some of the very reasons why it could never be considered a parable.[7]
Conclusion
I am fully convinced that Jonah should be read as history and not as a work of fiction or a parable. In addition to the compelling reasons listed above, the most powerful evidence is the way that Christ himself referred to Jonah. Jesus compared his own death, burial, and resurrection to the ordeal of Jonah in the whale, and he referred to it as a "sign." Just as Jonah was a sign to the Ninevites, Jesus was a sign to his own generation (Luke 11:30). The miraculous sign of Jonah being swallowed by a whale and regurgitated was likely instrumental in Nineveh's mass repentance.[8] If it did not actually happen, then why would Jesus compare the miracle of his actual resurrection to a sign that was not real?
[1] Douglas Judisch, "The Historicity of Jonah," Concordia Theological Quarterly 63, no. 2 (April 1999): 146.
[2] Paul J. N. Lawrence, "Assyrian Nobles and the Book of Jonah," Tyndale Bulletin 37 (1986): 121.
[3] Jay Lemanski, "Jonah's Nineveh," Concordia Journal (January 1992): 42.
[4] Ibid.
[5] Judisch, "The Historicity of Jonah," 149.
[6] Ibid., 152.
[7] Ibid.
[8] Eugene H. Merrill, "The Sign of Jonah," Journal of the Evangelical Theological Society 23, no. 1 (March 1980): 29.
Bibliography
Judisch, Douglas. "The Historicity of Jonah." Concordia Theological Quarterly 63, no. 2 (April 1999): 144-157.
Lawrence, Paul J. N. "Assyrian Nobles and the Book of Jonah." Tyndale Bulletin 37 (1986): 121-132.
Lemanski, Jay. "Jonah's Nineveh." Concordia Journal (January 1992): 40-49.
Merrill, Eugene H. "The Sign of Jonah." Journal of the Evangelical Theological Society 23, no. 1 (March 1980): 23-30.