Both Foster and I noted that there is an important distinction between a tax and a price. Professor Gordon is right that a tax on carbon affects the price of carbon--neither Foster nor I had ever maintained that it didn't.
But that doesn't mean that a tax is the same as a price.
And if Professor Gordon was trying to persuade readers that he sees the difference, he has failed miserably. Indeed, his response suggests that he comes close to equating the two.