Dramatic Irony and Social Commentary
Ever wondered how a playwright can make you cringe with just one line? Priestley does exactly this with Birling's famous "unsinkable, absolutely unsinkable" comment about the Titanic.
This creates brilliant dramatic irony because the audience knows the ship actually sank in 1912. Back then, this would have been even more shocking since people still remembered the tragedy vividly. The Titanic becomes a clever allegory for social class - the upper class survived on top whilst the working class perished below.
Birling's other key quote, "A man has to mind his own business and look after himself," perfectly captures his selfish, capitalist worldview. He believes in looking out for number one rather than helping others - exactly the attitude Priestley wants to criticise.
Quick Tip: Remember that Birling represents everything Priestley thinks is wrong with society - selfishness, greed, and ignoring social responsibility.