change any of the two things to make the classifier happy now usually we're concerned with changing the label it's like tell me which other label do I need to input to make you happy and if we make the labels differentiable of course we never input the true label we actually input like a distribution softmax distribution over labels and that's a differentiable we can use gradient descent to update the dog label we can use gradient descent to find the label that would make the energy function more happy so we could use