Irony is not that hard to understand, and yet so many people refer to something as ‘ironic’ or say ‘the irony of the situation’ where there is no trace of irony.
Take for example the song “Ironic” by Alanis Morissette: None of the situations described by Morissette are in fact ironic, just annoying or bad luck. In fact the only irony of the song is that there is no irony in it. Which either makes the writer an idiot or a genius. (Guess which one I am voting for.)
Verbal Irony occurs when the words used imply an opposite meaning to the literal meaning. (“I love being sick. It is so much fun.”)
Situational Irony occurs when the effect of actions is the opposite of what is intended. (I turn on a torch to see better, and end up blinding myself.)
Irony in literature and theatre usually involves the audience or reader having information that is not available to the character(s). This creates a tension for us as we note the character acting in a way that will have the opposite effect to what he intends, or being motivated by facts we know will be proved to be untrue.
In Othello and Romeo and Juliet we, the audience, know that Desdemona is faithful to Othello, and that Juliet is merely sleeping. Othello and Romeo are not in possession of this truth, and thus act to cause tragedy. In both cases the irony is that they are creating a tragedy they already believe is existing.
In Forrest Gump, we can see how his interaction with characters in history changed the world. Forrest Gump has no such knowledge. The irony is not that his actions are different from what he intends, but that we are aware of the effect(s) which he is not. This is dramatic irony.
Another example of Irony that is relevant to fiction would be metafiction. Metafiction (also called Romantic Irony) involves reminders that the story is in fact a story. Examples would be the author, or even the characters, commenting on the fact that they are in a story, or drawing attention to plot devices.
Bad luck and stupidity are not irony. William Bullock invented the rotary printing press, and then was later killed in an accident with one. This is irony, because had he not invented it, it could not have killed him. The irony relies on the fact that this was unexpected. A man who invents a new type of parachute, and dies testing it is not irony. It is bad luck. The fact that the parachute needed to be tested in a potentially life-threatening manner removes the irony.
If however the inventor was walking down the street, and a random stranger fell on top of him due to a failure of the parachute to open… that would be irony.
So for instance Alanis Morissette singing about “10,000 spoons, when all you need is a knife” is not ironic, just annoying. Unless of course you need a knife to open a box that happens to contain 10,000 knives. Then it would be ironic.
I said at the beginning that irony was easy.
I may have lied a little.
But that wasn’t irony.