This theme is closely related to those of myth making and imagination. Synge says in the Preface to The Playboy of the Western World, "In Ireland ... we have a popular imagination that is fiery and magnificent, and tender ...." It is this imagination that undergirds considerations of fantasy and reality. Myth making depends upon imagination and thus inevitably causes a disjunction with reality.
In the play the creation of contemporary myth around Christy explodes as the villagers' imaginations fill in the missing details of his story, then turn the skeleton of his confession into an epic with Christy as the hero cast in a Byronic type.
Bravery's a treasure in a lonesome place, and a lad would kill his father, I'm thinking, would face a foxy divil with a pitchpike on the flags of hell.
It's the truth they're saying, and if I'd that lad in the house, I wouldn't be fearing the loosed kharki cut-throats, or the walking dead.
When Mr. Mahon storms onto the scene to hunt down his son, reality clashes forcefully with the myth built from imagination. Nonetheless, the villagers continue in the confines of imagination by creating anti-myths as they prepare to cut Christy's life off for his unspeakable deed (of thinking he killed his father--twice ...).
In the end, Christy appropriates the myth as his own even while the villagers reject it. Thus he outlines a new reality for himself with a self-composed new myth as its bedrock, thereby creating the ultimate clash of fantasy versus reality in which fantasy ironically inspires reality.
You're blowing for to torture me (His voice rising and growing stronger.) That's your kind, is it? Then let the lot of you be wary, for, if I've to face the gallows, I'll have a gay march down, I tell you, and shed the blood of some of you before I die.
Ten thousand blessings upon all that's here, for you've turned me a likely gaffer in the end of all, the way I'll go romancing through a romping lifetime from this hour to the dawning of the judgment day. [He goes out.]