 What Beardsley says here is basically correct. To show that the intentional fallacy is indeed a fallacy, however, to show that (C) isn’t criterial evidence for (D), the premise concerning the author’s intention should be assumed to be true, and the strength of the inference gauged on that assumption. If a fallacy has indeed been committed, the premise, considered simply by itself, will lend no support to the conclusion. But instead of examining the case of Humpty Dumpty as just indicated, Beardsley questions the truth of the premise, and correctly finds it wanting. That isn’t to the point.