If someone has seen all shades of blue except one, and is presented with a spectrum of blue with this shade missing, using their imagination, they will be able to form an idea of that shadow. Since this idea was not copied from an impression, it contradicts the principle. Hume rejects the example as something irrelevant, even though we know it is not. If this counterexample of forming an idea without deriving from an impression is possible, will it be possible for us to form other ideas without previous impressions? This question is important, because Hume repeatedly uses his principle in his philosophy to test ideas. I think this is an appropriate response, as this champion is so unique. The possibility of unjustifying its principle is