What distinction did David Hume make between impressions and ideas?

David Hume distinguished between two types of perceptions: impressions and ideas. He defined impressions as perceptions that the mind experiences with the greatest force and violence, such as sensations or feelings. In contrast, ideas are the "faint images" or copies of these impressions, which occur when we think or reflect.1

In his work A Treatise of Human Nature, Hume summarized this distinction by noting that impressions are felt, while ideas are thought. He posited that for every simple impression, there is a corresponding simple idea that differs only in its degree of force and vivacity. Furthermore, Hume argued that simple impressions are the causes of their corresponding simple ideas, as the formation of a simple idea is always preceded by the experience of the impression.1

While Hume acknowledged that rare states like madness or fever might blur these lines, he maintained that the distinction is fundamental to understanding the contents of the human mind.12