In many respects, Aesop’s Fables are allegories, where you would define ‘fable’ as a story with a lesson attached. Same with Christ’s parables. And this is what made allegories so popular as vehicles for communicating complex ideas of sin and redemption in medieval times. But the story vehicle needs to be entertaining enough to stand up on its own, or nobody will listen and the message will be lost.
This drive to educate through simplification tends to deal in essences but again, unlike the symbol, with communicable essences. I remember once interviewing Justin Hayward of the Moody Blues, who released the fabulously pretentious album ‘Days of Future Passed’ in (when else?) 1967. It was one of the first ‘concept’ LP’s , and they dragged in some unfortunate musical arranger to help them orchestrate their songs. Hayward remembered asking the poor bugger if a particular passage could “sound more purple”, thus revealing himself to be a symbolist by inclination. An allegorist would have made up a story to illustrate what he meant by purple - that is, if he was determined to illustrate a quality so abstract, which he probably wouldn’t have been. So a further comparison we can make, courtesy of the Moodies, concerns the compactness of the symbol versus the allegory.
But I digress. In some societies, fables, parables and allegories were grouped together to form a joined-up code of morality or ethics applicable to everyone. The stories were therefore given an added dimension that propelled them outside their immediate cultural context, both geographically and temporally. By implication, again to quote CS Lewis’s ideas, they then belonged not just to one society but any society that contained humans. The stories spoke to mankind, emphasizing shared facets of his experience understandable to all - wherever and whenever. In some respects, most allegories are the bastard children of the Ten Commandments, except that they’re not couched in the form of laws or bald imperatives. Novelist and structuralist philosopher Umberto Eco noted that this web of allegories comprised:
 
a kind of alphabet through which God spoke to men and revealed the order in things , the blessings of the supernatural, how to conduct oneself in the midst of this divine order and how to win heaven. In themselves, things might inspire distrust because of their disorder, their frailty, their seemingly hostility. But things were more than they seemed. Things were signs. Hope was restored to the world because the world was God’s discourse to man.
Approaching the allegory from a structuralist perspective, he would say that, wouldn’t he? Everything signifies something else, which is the way structuralists see the world. But when discussing medieval allegory, he’s absolutely correct. The questing Knights of the Round Table were continually educated by aspects of their physical landscape, or by small dramas which were laid on within it designed to edify and instruct them as they searched for The Truth. John Bunyan’s ‘Pilgrim’s Progress’ uses much the same technique by representing life as an allegorical journey of the spirit towards wisdom, as does Langland’s ‘Piers Plowman’. I could go on.
These days, we like to think ourselves a bit more sophisticated than the average Medieval peasant, so allegory isn’t as popular as it once was. That doesn’t stop critics trying to characterize more recent works such as ‘Doctor Jekyll and Mr Hyde’ as an allegory of the struggle between good and evil in man, but there’s a general feeling that to describe something as allegorical may not be doing the story justice - it may have more far-reaching ambitions for its meaning than an allegory can accommodate. Vladimir Nabokov got very shirty about those who branded Franz Kafka’s novels as allegories, which, he said, was tantamount to reducing ‘Metamorphosis’ to an entomological curiosity.
But then there’s ‘Animal Farm’, perhaps the best known political allegory ever written. ‘Animal Farm’ is strongly allegorical, but it represents a finely judged balance between not two, but three levels of meaning: the literal level which houses the immediate story of the animals; the secondary level  that comments on the totalitarian politics of Soviet Russia, and a third that argues that these specific men possess the qualities of all leaders who rely on repression and manipulation in order to become successful.
 
 
And that, ladies and gentleman, is your allegory. What we need to take with us from this section is the broad application of the allegory’s meaning, meaning that encourages the idea that all mankind is governed by common urges, thoughts and experiences. Which leads us seamlessly into a consideration of:
 
 Myth - When F. Scott Fitzgerald first arrived at Princeton University in 1913, he was absolutely smitten with the antiquity of the buildings. “Here,” he wrote in 1927, “is no monotony, no feeling that it was all built yesterday at the whim of last week’s millionaire.” And yet it was. In fact, although the paint was scarcely dry on the “great dreaming spires of Holder and Cleveland towers”,  he still  viewed them through the misty lens of a fin de siecle romanticism that made the buildings appear preposterously old. And this perfectly encapsulates the two most important facets of Myth - its curious relationship with truth, and an assumed universal significance, which, like the towers at Princeton, can quite easily prove illusory.
Once again, I’m afraid I’m going to stray into OED mode for this section, since the literary application of myth differs considerably from what’s commonly conceived when using the word. Most of the time, we understand ‘myth’ by its received definition of “a purely fictitious narrative”, a sense it seems to have inherited during the Victorian era. Prior to that, it was looked on as a story involving gods and goddesses with the emphasis firmly placed on its fantastical elements and not whether it was true or not. Unless you were an Ancient Greek, you’d probably realize that the myth of Leda and the Swan was pure fiction, to the point where this didn’t even need saying. The Victorians, however, being rather anal about these matters, probably didn’t want there to be the slightest possibility that some misguided individual might take it literally, so the word ‘myth’ became synonymous with lying.
Somewhere along the way, however, myth also became involved with the universal truths we were looking at a second ago in allegory, although nowhere in the OED is there any allusion to this shade of meaning, which is rather odd. Collins nods in the direction of myth being involved with social mores and their origins, but proceeds no further.
Yet George Eliot understood this sense of the word, to denote mankind’s shared spiritual inheritance. In ‘Middlemarch’ the aging and ailing Reverend Casaubon is engaged in his lifetime’s work entitled ‘The Key to All Mythologies’, which, when completed, would offer a complete and convincing explanation of why mankind has developed the way it has. A modest proposal, clearly, but pretty much from the word go, we’re given the impression it’s a project doomed to failure, and by the middle of the novel his young wife Dorothea knows it too:
 
It was clear enough to her that he would expect her to devote herself to sifting those mixed heaps of material, which were to be the doubtful illustration of principles still more doubtful. The poor child had become altogether unbelieving as to the trustworthiness of that Key which had made the ambition and the labor of her husband's life. It was not wonderful that, in spite of her small instruction, her judgment in this matter was truer than his: for she looked with unbiased comparison and healthy sense at probabilities on which he had risked all his egoism. And now she pictured to herself the days, and months, and years which she must spend in sorting what might be called shattered mummies, and fragments of a tradition which was itself a mosaic wrought from crushed ruins--sorting them as food for a theory which was already withered in the birth like an elfin child. Doubtless a vigorous error vigorously pursued has kept the embryos of truth a-breathing: the quest of gold being at the same time a questioning of substances, the body of chemistry is prepared for its soul, and Lavoisier is born. But Mr. Casaubon's theory of the elements which made the seed of all tradition was not likely to bruise itself unawares against discoveries: it floated among flexible conjectures no more solid than those etymologies which seemed strong because of likeness in sound until it was shown that likeness in sound made them impossible: it was a method of interpretation which was not tested by the necessity of forming anything which had sharper collisions than an elaborate notion of Gog and Magog: it was as free from interruption as a plan for threading the stars together. And Dorothea had so often had to check her weariness and impatience over this questionable riddle-guessing, as it revealed itself to her instead of the fellowship in high knowledge which was to make life worthier!
 
What Casaubon thinks he’s doing is researching a sort of Ultimate History of Man, raising supposition to the rank of certainty as he goes along. Before the possibilities of mapping the brain, or cataloguing every strain of DNA in the human body presented themselves, this was the perhaps the only plausible route to get to know the Meaning of Life - through comparative anthropology, by comparing the rites and customs of different social and ethnic groups from all over the world and determining what they have in common. That way scholars (who, like Casaubon, were often minor clerics with too much leisure time between services) could try and explain why we are as we are.
Strange that devotees of religion should take this task on their shoulders, since any conclusion they might draw from this anthropocentric study were almost bound to lead away from God.
Anthropology was certainly the chosen line of attack for Sir James Frazer, when he began to publish his hugely influential masterwork ‘The Golden Bough’ in 1890. But Sir James wasn’t about to fall into the same trap as the Rev Casaubon - his empirical ambitions are far more modest. In the introduction to his thesis, he wrote:
 
If we can show that a barbarous custom, like that of the priesthood of Nemi, has existed elsewhere; if we can detect the motives which led to its institution; if we can prove that these motives have operated widely, perhaps universally, in human society, producing in varied circumstances a variety of institutions specifically different but generically alike; if we can show, lastly, that these very motives, with some of their derivative institutions, were actually at work in classical antiquity; then we may fairly infer that at a remoter age the same motives gave birth to the priesthood of Nemi. Such an inference, in default of direct evidence as to how the priesthood did actually arise, can never amount to demonstration. But it will be more or less probable according to the degree of completeness with which it fulfils the conditions I have indicated. The object of this book is, by meeting these conditions, to offer a fairly probable explanation of the priesthood of Nemi [itals mine].
 
This introduction to one of the later editions of ‘The Golden Bough’ was written in response to critics who thought Frazer had bitten off more than he could chew and that it was, in fact, hugely presumptive of anyone to try and understand the Mysteries of Human Existence. Frazer denied he was doing any such thing (at least in his Introduction), just making a few connections here and there, and drawing some ‘fairly probable’ conclusions. But us students of meaning are always looking for something more than the ‘fairly probable’, and in myth, we found it in spades.