# Section I: Of Scepticism with Regard to Reason explained — A Treatise of Human Nature > Chapter companion for A Treatise of Human Nature by David Hume. ## What happens Hume argues that all knowledge, including demonstrative reasoning, degenerates into probability due to the fallibility of human faculties. He introduces the idea that reason must be checked by a meta-judgment about its own reliability, leading to an infinite regress of probabilities. However, he notes that nature prevents total skepticism by making subtle reasoning less convincing as it becomes more complex, thus preserving belief in common life. ## Themes in this chapter ### Skepticism About the External World Hume extends skepticism to reason itself, arguing that all knowledge reduces to probability, undermining certainty in demonstrative sciences. ### Custom and General Rules Belief is maintained by natural and easy conceptions, and the force of reasoning diminishes with complexity, showing the role of custom in preserving conviction. ## Character check-ins ### David Hume Author and narrator, presenting arguments on skepticism and the nature of belief. ## Key lines > Reason first appears in possession of the throne, prescribing laws, and imposing maxims, with an absolute sway and authority. Her enemy, therefore, is obliged to take shelter under her protection, and by making use of rational arguments to prove the fallaciousness and imbecility of reason, produces, in a manner, a patent under her and seal. Reason initially seems all-powerful, but skepticism uses rational arguments to undermine reason, gaining legitimacy from reason itself. _Hume describes the paradoxical nature of skeptical reasoning._ > By this means all knowledge degenerates into probability; and this probability is greater or less, according to our experience of the veracity or deceitfulness of our understanding, and according to the simplicity or intricacy of the question. Because our faculties are fallible, even demonstrative reasoning only yields probable conclusions, with the degree of probability depending on our past experience and the complexity of the issue. _Hume's central claim that knowledge becomes probability._ > The same argument, which would have been esteemed convincing in a reasoning concerning history or politics, has little or no influence in these abstruser subjects, even though it be perfectly comprehended; and that because there is required a study and an effort of thought, in order to its being comprehended: And this effort of thought disturbs the operation of our sentiments, on which the belief depends. Arguments that are persuasive in everyday matters lose their force in abstract philosophy because the mental effort required to grasp them interferes with the natural sentiments that produce belief. _Hume explains why subtle reasoning fails to convince._ ## Links - HTML: https://www.betterreads.online/discover/a_treatise_of_human_nature_se/chapters/section-i-of-scepticism-with-regard-to-reason - Book: https://www.betterreads.online/discover/a_treatise_of_human_nature_se - All chapters: https://www.betterreads.online/discover/a_treatise_of_human_nature_se/chapters