Allegory and symbolism aren't exactly the same ...
I did some research before posting this Q&A, and found many different online discussions of the difference between allegory and symbolism. From Quora, for example:
A symbol is something that represents something else, usually greater than itself (e.g., a tree can be a symbol of life).
Allegories are narratives that have a symbolic meaning, like fables or parables.They represent some aspect of life, or life itself, and contain symbols.
Aesop's fable of the ant and the grasshopper is an allegory of the importance of hard work and planning for the future. The ant is a symbol of industry and prevision.
Essentially, it seems that both are based on the same idea (one thing representing another), but an allegory is an entire story set up to symbolise something different, while a symbol is more likely to be an object within the story.
... but we've been using symbolism in a very broad way.
Our questions tagged with symbolism include not only ones about symbolic objects (e.g. What does the sukebind represent? or What is the greater meaning of the thrush?) but also ones about symbolism on a wider scale: symbolism of actions, events, or even entire works, such as What is the significance of the fact that the covered wagons were traveling East at the end of Atlas Shrugged? or Is there any deeper significance to Borges's "The South"? or What's the significance of the witches' name change in Sandman?
There were some recent comments about this sort of issue between myself, Hamlet, and DVK on one of my questions, but they seem to have been deleted. If I recall correctly, Hamlet was arguing that "symbolism" should only refer to symbolic objects and not to actions or events. But the usage so far of the symbolism tag (our most used tag!) tells a different story.
Funnily enough, one of the two allegory questions, What did the Roll which the Shining Ones delivered to Christian represent?, is actually about what is represented by a particular object, so I doubt anyone would disagree that it should be tagged symbolism.
So the question is: do we want to differentiate between allegory and symbolism in our tags?
Having two separate tags for these two notions would require explaining the difference clearly in the tag wiki excerpts, editing probably a few dozen existing questions, and continuing to retag new questions as they come in because many people still won't get the difference between allegory and symbolism. Rolling the two into one would be more consistent with existing practice and would make curation easier going forwards.
And after all, the two concepts are closely related: we're not talking about putting two completely different things under the same header just for ease of administration. Actions, events, or entire stories can be symbolic even if it would be strange to refer to them as symbols; and the name of the main tag is symbolism, not symbols.
However, we should definitely keep allegory as a synonym, so that people who type
allegory into the tag box will use the right tag rather than recreating a different one over and over again. So: