# Section III: Why a Cause Is Always Necessary explained — A Treatise of Human Nature > Chapter companion for A Treatise of Human Nature by David Hume. ## What happens Hume challenges the common philosophical maxim that everything which begins to exist must have a cause. He argues that this proposition is neither intuitively nor demonstrably certain, as it is not based on any of the infallible relations of ideas. He refutes several common arguments for the necessity of a cause, showing they all presuppose what they attempt to prove. He concludes that the belief in the necessity of a cause arises from observation and experience, not from reason, and sets the stage for his future inquiry into how experience gives rise to this principle. ## Themes in this chapter ### Skepticism About the External World Hume questions the intuitive certainty of the causal principle, suggesting that our belief in causality is not grounded in reason but in custom and experience. ### Custom and General Rules Hume argues that the opinion of the necessity of a cause arises from observation and experience, hinting at the role of custom in forming such beliefs. ## Character check-ins ### David Hume Author and narrator, critically examining the principle that every beginning of existence requires a cause. ## Key lines > It is a general maxim in philosophy, that whatever begins to exist, must have a cause of existence. Philosophers commonly assume that everything that comes into being must have a cause. _Hume introduces the principle he will challenge._ > All certainty arises from the comparison of ideas, and from the discovery of such relations as are unalterable, so long as the ideas continue the same. Certainty comes from comparing ideas and finding relations that never change as long as the ideas remain the same. _Hume outlines his theory of knowledge to show that the causal maxim lacks intuitive certainty._ > The separation, therefore, of the idea of a cause from that of a beginning of existence, is plainly possible for the imagination; and consequently the actual separation of these objects is so far possible, that it implies no contradiction nor absurdity. We can easily imagine something beginning to exist without a cause, so there is no contradiction in such a separation. _Hume argues that the causal principle is not demonstrable because distinct ideas are separable._ > But to say that anything is produced, or to express myself more properly, comes into existence, without a cause, is not to affirm, that it is itself its own cause; but on the contrary in excluding all external causes, excludes a fortiori the thing itself, which is created. Saying something comes into existence without a cause does not mean it is its own cause; rather, it excludes all causes, including itself. _Hume refutes the argument that denying a cause implies self-causation._ > Since it is not from knowledge or any scientific reasoning, that we derive the opinion of the necessity of a cause to every new production, that opinion must necessarily arise from observation and experience. Our belief that every new thing needs a cause comes from experience, not from reason or knowledge. _Hume concludes that the causal principle is based on experience, not a priori reasoning._ ## Links - HTML: https://www.betterreads.online/discover/a_treatise_of_human_nature_se/chapters/section-iii-why-a-cause-is-always-necessary - 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