Hume’s Science of Human Nature: Scientific Realism, Reason, and Substantial Explanation by David Landy (review)

As the title suggests, David Landy’s Hume’s Science of Human Nature: Scientific Realism, Reason, and Substantial Explanation defends a staunchly realist interpretation of Hume on scientific explanation. Landy’s forward-looking view sees Hume’s methodology in the Treatise as anticipating developments much later in history. He gives Hume a Sellarsian update, making his philosophy of science more impactful and contemporary than previously thought. The motivation for his view is twofold. First, he wants to respond to the long line of Hume critics who think his “science of human nature” is hardly science at all. According to this interpretive tradition (the Deductive-Nomological view), Hume’s “science” is merely the collection of empirical generalizations with no explanation involved. Far from deploying this lazy, shallow method, Landy’s Hume has a sophisticated methodology at the heart of which is a “perceptible model.” Just as Bohr proposed that we understand the structure of an atom (not directly observable) as analogous to the solar system (directly observable), Hume is best understood as treating simple ideas as theoretical posits in an experiential model based on purely descriptive phenomenology that both resemble and differ from direct experience. Secondly, Landy wants to distance himself from other recent attempts to update our understanding of Hume on scientific explanation, most notably the New Humean view. While Landy and the New Humeans agree that Hume intends to do more than collect generalizations, the New Humeans think Hume concludes that a satisfying explanation is impossible, as the explanans is unknowable. The Deductive-Nomological view sees Hume as failing to reach for substantial explanation. The New Humean view sees Hume as failing to grasp substantial explanation. Landy’s interpretation has Hume reaching for substantial explanation and it aligns Hume’s grasp with his reach.

Chapters 1 and 2 lay out Landy’s perceptible model-based interpretation. He begins with Hume’s theory of mental representation, introducing the basic distinctions between simple and complex perceptions and between impressions and ideas, but then quickly treks into controversial territory. Landy elucidates something about which Hume is not explicit but which he likely cannot deny. We never experience simple ideas as simple. Experience is always complex. Simple impressions always enter the mind as parts of complex impressions. Because experience is always complex, our revival set for “simple idea” consists exclusively of complex ideas. What does this mean for the status of simple ideas? Simple ideas are like atoms. We cannot see them but we commit to them as theoretical posits because they make sense of what we do see. Landy sees us as having a choice. Explain the novelty of human thought and give up strict nominalism or give up a satisfying explanation of the novelty of human thought and keep strict nominalism. Experience alone licenses only nominalism, but to properly explain experience, you cannot be a strict nominalist. Landy opts to give up strict nominalism by construing simple ideas as unobservable theoretical posits. By basing them on a perceptible model, he minimizes the risks posed to Hume’s naturalism. As for substantial explanation, Landy argues that Hume takes no issue with substantial explanation per se. His problem, Landy explains, is with substantial explanation of inappropriate putative objects of explanation. Hume rejects and strongly condemns non-empirical methods. If a substantial explanation is explaining a bona fide empirical phenomenon, there is no problem by Hume’s lights.

Chapter 3 offers a deeper analysis of Hume on substantial explanation and explores the role of reason. Because Hume’s science of human nature is so rich and covers such an array of experience, it can be difficult to track Hume’s own ontological commitments. The vulgar and especially the false philosopher often talk of the substance undergirding human experience, but Hume clearly denies the legitimacy of their claims. They are not advancing anything like an acceptable substantial explanation of descriptive...