How did Hume explain the limits of knowledge about the external world?

In the context of modern philosophy, David Hume explained the limits of knowledge regarding the external world through his commitment to empiricism, which posits that all human knowledge is derived from sense experience.12

Hume argued that the human mind is confined to its own impressions (vivid sensory experiences) and ideas (faint copies of those impressions). Because we only have direct access to these mental states, we cannot compare an idea with an external object to verify its accuracy. Consequently, he concluded that it is impossible to have rational knowledge of anything existing beyond our immediate experience.3421

Furthermore, Hume challenged the notion of substance, arguing that we have no impression of a "hidden substratum" underlying an object's properties. He viewed objects and even the "self" as mere collections of perceptions united by the imagination. While he acknowledged that humans naturally believe in an external world, he maintained that such beliefs are not rationally justified by reason or empirical observation, but are instead inextinguishable propensities of human nature necessary for survival.5267