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Message: [QUOTE="Simen Edvardsen, post: 4528036"] The problem with #respond_to? is that it only tells you that a method is supported. It doesn't tell you whether the method takes arguments that quack like the ones you want to pass, or that the return value behaves what you like. In other words, you'll have to trust that the method behaves how you'd like to. Imagine: def make_peace(world) world.create_piece if world.respond_to? :create_piece end class World def make_piece(means = War) means.use! self end end Now make_peace (called with a World) will actually start a war. See the problem? #respond_to? will only tell you that a method is supported, but not that it behaves how you'd like (not that static typing guarantees this either). It saves you from NoMethodError, but not any other error. Duck typing is trusting other objects to do the right thing, and #respond_to? isn't all that useful in that regard. [/QUOTE]