For such a well-known and irritating proverb, the phrase ‘don’t judge a book by its cover’ is surprisingly young. It’s thought to be a derivation of a passage from the 1944 edition of the African journal American Speech: “You can’t judge a book by its binding.” Two years later, it appears in a more familiar form in Fuller and Rolfe’s Murder in the Glass Room: “You can never tell a book by its cover.”

It’s less surprising when you consider that illustrated book covers are a relatively recent phenomenon. It wasn't until the end of the 19th century, with consumer demand for cheap books skyrocketing, that British publishers slowly began to realise how useful illustrated covers could be in promoting the books they contained, and in providing useful advertising space for other publications. Over time, covers became increasingly decorative. This marked a departure from the 18th and 19th centuries, where generic yet ornate and exquisite leather bindings reflected the wealth and status of the owner. Unlike the new ‘buy me!’ initiative, these covers had asked beholders not to judge the book within, but instead the reader. So the process of literally judging a book by its cover is actually quite new.

The wisdom behind the proverb, though, is timeless, replying to the idea that the outside of something may not always reflect the inside. The doctrine that ‘it’s what’s inside that counts’ is a potent and widely accepted one, and one we rely upon for optimism when we apply it to other things, and self-confidence when we’re thinking about our own ‘covers’.

Yet, in the figurative sense, people have always judged books by their covers. Psychologists attest that it is a very difficult thing not to do: visual processing neurones constitute roughly 30 per cent of our cortex overall. Our brains predispose us to judging most things by their outward appearance: food, books, people. So, as Alex Lickerman puts it, “[t]he wrappers in which things come not only powerfully affect what interests us but also how we react to the contents we find inside”. The link between visual perception and evaluation is unavoidable. While we might assume it’s true that the best books merit the most meticulous attention from publishers and designers, there’s a real risk of undervaluing a good book if its cover disagrees with you – or, most likely, of never picking it up in the first place.

Perhaps whether or not we should judge books by their covers depends whether or not we can actually do it with any accuracy. Conveniently for the purposes of this article, goodreads.com have developed an online test which tells you exactly how good you are at judging a book by its cover. The test shows you 10 sample covers, which you have to rate using their customary five-star system. It then compares your rating to the average rating given by online reviewers of the book. (Admittedly, there may well be some self-selection bias here: I was quite good at judging said books by their covers – although whether this is because I am an astute, fair and perceptive individual, or whether I match the demographic of the average goodreads reviewer, I couldn’t possibly say.)

I would recommend trying this; it’s a process which teaches you a startling amount about your own prejudices when it comes to literature. It’s probably a clue to the fact that I mostly read canonical literature (more on this horrific term in a few weeks) that my overwhelming typeface preferences are serif fonts (ideally Times New Roman). Meanwhile, anything looking vaguely new-age techno immediately recalls Alex Rider, which is a bad thing when the blurb heralds it as a modern-day Pride and Prejudice. Cartoons, too, are a no-no unless they are beautiful and stylised enough not to have been put there simply on the basis of being completely generic. That’s a test failed by the upturned cartoon pig on the cover of Cleaving: a story of Marriage, Meat and Obsession.

If this kind of visual snobbery makes for sad reading, it’s worth remembering that we probably have a right to expect books’ covers to reflect something of their inner quality, in a way that we don’t with, say, our friends. Furthermore, the distinction between the ‘outside’ and ‘inside’ of a book is not always as marked as we think. Authors are very often involved in the design process. They almost always choose the title, whose influence on the reader must be at least equal to the cover design. No matter how stylish, sophisticated and beautiful the cover, I would never have been convinced by Notting Hell or Fat Vampire: A Never Coming Of Age Story.

We cannot avoid judging books by their covers – but, as long as we’re aware of it, that’s not necessarily a bad thing. But the next time you’re in a bookshop, think about what your reaction to certain books might suggest about you.