"The Sake of Argument", by Randall Munroe, licensed under Creative Commons Attribution-NonCommercial 2.5 License
'It's not actually ... it's a DEVICE for EXPLORING a PLAUSIBLE REALITY that's not the one we're in, to gain a broader understanding about it.' 'oh, like a boat!' '...' 'Just for the sake of argument, we should get a boat! You can invite the Devil, too, if you want.'