Abstract: The “Hume's Problem” reveals the huge gap between “is” and “ought”,leaving a difficult problem pointing to agnosticism.Starting from “practice,that is,experiment and industry”,Engels refuted Hume's agnosticism and added a link of “able” between “is” and “ought”,thus forming a new logical relationship chain which is about “is-able-ought”.This provides us with an innovative theoretical perspective which helps us to re-understand the importance of Aristotle's question of “production” and the profound meaning of Hegel's famous proposition that “everything that is realistic is rational,and everything that is rational is realistic”.This will also help us to correctly understand the link of “able” that most often causes cognitive fuzziness and confusion in reality,and correctly deal with the relationship which is about “is-able-ought”,so as to reduce all kinds of errors in judgment and action.

Key words: Hume's Problem, is, able, ought