Toleration is obligatory, not criticism. Encouragement of the critical attitude is wise. The best way for it is helping people learn to distinguish between appropriate and inappropriate criticism. Now, criticism is never final: no criticism is unanswerable. What criticism and what answer is inappropriate can be debated; if debates on this falter, it is better to give up. Nevertheless, it is advisable to take for granted that some moves are inappropriate. Examples: to bow to authority or to common knowledge; to ascribe to opponents opinions that they reject while ignoring this rejection; to borrow ideas from opponents without saying so; to seem to argue against an idea while arguing for an idea; to refuse to clarify; to demand excessive clarification; and so on. It is particularly improper to demand that critics offer alternative views, since their criticism may be valid even if they have no alternative. If alternatives are offered it is particularly improper to criticize them as vindications of some view, since both can be erroneous. The main contention of Popper’s popular critics against him is their demand that criticism should be constructive.