What is the theme in Dancing at Lughnasa by Brian Friel?

Memory is a central theme of Friel's play is memory. The action of the play, which takes place in the later summer of 1936, is framed as a depiction of Michael's memories of his childhood. In his closing monologue, the character of Michael as a young man explains the significance of these memories:

And so, when I cast my mind back to that summer of 1936, different kinds of memories offer themselves to me. But there is one memory of that Lughnasa time that visits me most often; and what fascinates me about that memory is that it owes nothing to fact. In that memory atmosphere is more real than incident and everything is simultaneously actual and illusory. In that memory, too, the air is nostalgic with the music of the thirties.