The Reading Room

Reflecting on Banned Books: Hume’s Enquiry Concerning Human Understanding

Britain, 1761. All of David Hume’s works are banned by the Index Librorum Prohibitorum, including his 1748 Enquiry Concerning Human Understanding. What was so horrible about the work of this Scottish philosopher that would make the authorities scared of people reading it?  
Of course, there need not be anything actually bad for a book to get banned.  It’s usually sufficient that it contain ideas which someone finds threatening. And in 18th-Century Britain, there was no shortage of dangerous ideas. Some of these ideas entered the arena of Things Respectable People Might Debate, such as Smith’s arguments against mercantilism. Although a threat to particular commercial interests, legislators found that they could benefit from these new ideas, and so they allowed to be discussed. But Hume had ideas that were – or at least were perceived as being – dangerous to the entirety of society.
Hume’s Enquiry is a treatment of metaphysical and epistemological theories, part of the grand conversation of 17th- and 18th-century philosophy, from Descartes and Spinoza and Leibniz in Continental Europe to Hume’s fellow British thinkers John Locke and George Berkeley. The continental thinkers came to be known as “the rationalists” while the British thinkers came to be known as “the empiricists.” For the rationalists, all knowledge comes from the mind, not from sense perception. The British tradition challenged that notion, and argued that knowledge begins in sense perception. Locke had argued, contrary to Descartes, that the mind contains no innate ideas and could be thought of as a “blank slate.” Hume took Lockean empiricism to its ultimate conclusion, and, odd as it sounds to the 21st century reader, this rendered conclusions which were seen as threats to the social order.
According to Hume, the contents of our minds include “ideas” and “impressions,” the latter being more fundamental.  Impressions are the sensory inputs we receive, and the basis of ideas we develop. He argued that there can be no idea without an impression – more precisely, that there can no coherent idea without it being based on an impression. We can imagine things that do not exist because we can imagine their component parts. For example, no one has ever seen a blue polar bear, but we can form an idea about blue polar bears because we have impressions of polar bears and of blue things.  But how is this anodyne epistemology exercise going to turn out to be so dangerous?
Hume’s theory of idea-formation means that a lot of things we’ve been taught to talk about are things we really don’t have any impressions of, for example causation. Hume’s empiricism casts doubt on our understanding of scientific method by obliging us to be more conservative about causal relations. He argues that we ascribe causality mainly because we perceive a regularity between alleged causes and their effect, but we never perceive the necessary connection that would make a true cause as opposed to regularly-occurring coincidence.
Even more threatening to the social order was that Hume’s theory of knowledge also implied that we have no impressions of souls, or of God, which means we don’t really have ideas about these things. We talk about them but don’t really know what we’re talking about. Hume was in fact an atheist, but while that alone might be excused as merely bad taste, having a rigorous philosophical account of why all talk of divinity is meaningless can only be seen as a threat to the social order.  
This passage, the last lines of the Enquiry, shows the forcefulness of Hume’s argument: “When we run over libraries, persuaded of these principles, what havoc must we make? If we take in our hand any volume; of divinity or school metaphysics, for instance; let us ask, Does it contain any abstract reasoning concerning quantity or number? No. Does it contain any experimental reasoning concerning matter of fact and existence? No. Commit it then to the flames: for it can contain nothing but sophistry and illusion.” Talk of immortal souls and divine beings looks like the sort of thing his framework categorizes as sophistry and illusion.  He explicitly rejects testimony about miracles. That’s what gets Hume on the banned book list. Of course, we can ask the proprietors of the Index Librorum Prohibitorum the same question about Hume as about anything else: why not let us read it? If it is full of error, we will discover it, or you can point it out. Let the arguments occur and the truth will prevail. We’ve moved away somewhat from banned book lists in the days since Hume, but, sadly, not far enough.