The David Hume essay “Enquiry Concerning Human Understanding” examines the scope, obviously, of the human understanding. Fundamentally, this Hume essay asks an epistemological question: “What can a human know? And how?”

Before diving into Hume’s work, an “understanding” of the context in which he wrote would be helpful. This Hume essay clearly responds to John Locke’s “An Essay Concerning Human Understanding,” as shown by the titles’ similarity to one another.

Locke, to crudely summarize, argued that humans possess the ability to develop several orders of subjective, or internal, ideas. However, the objective, or external, world “causes” the Lockean ideas. Therefore, the outside world influences the human brain in such a way that the human creates ideas that roughly correspond to the external world.

Although this summary insults Locke’s work, the Hume essay generally rejects that the human can know with certainty anything external to him because the notion of “cause and effect” is NOT empirical.

The Hume essay suggests that humans have “impressions” and “ideas,” but they are limited to the subject’s cognition. An external world may exist and a human certainly experiences affections from something or somewhere, but our knowledge of those affections is strictly internal.

Therefore, Hume’s “impressions” are where the affections meet the subject. The human develops “ideas” based on those impressions. The Hume essay justifies this by illustrating that Locke’s system depends on “cause and effect,” which is by no means empirical.

How is cause and effect NOT empirical? This work, if my memory stands, uses the analogy of billiards. In pool, the cue ball hits the eight ball, for example, and all we see is the cue ball pushing the eight ball.

Although this metaphor is simple, it is very telling because “cause and effect” can be found nowhere in this example. The Hume essay contends that we see Event A – the cue ball moving toward the eight ball – and Event B – the eight ball moving away. In other words, we only see a “correlation” of events never a direct causal relationship.

Hume advances this idea even further. Hume argues that the sun’s rising is equally uncertain. We merely assume that the sun rises everyday but we have nothing telling us that the sun will rise again tomorrow.

The essay again proceeds with this these notions and ultimately rejects any certainty in religion. In fact, the most certainty one can find in religion is through mere testimony. One’s testimony indicates veracity but never proves it. Thus, religion is victim to the limits of human knowledge.