A simile must be as precise as a slide-rule and as natural as the smell of dill.” I owe that pair of perfect similes to the Russian short-story writer Isaac Babel. I’ve been thinking a lot about similes and metaphors recently. Given the slim chance that any reader of this column doesn’t know what a metaphor is, it means applying the word for one object to a different object for effect, as in “he’s a worm” or “she’s a tiger”. Metaphors are important in computing, although most of us are unaware, most of the time, that what we’re doing is metaphorical.


The most obvious application of a metaphor in computing is the GUI, or graphical user interface, where objects on the screen mimic real-world objects and behave in analogous ways to their real-world counterparts. So you can click on a picture of a folder and it opens up; you can “grasp” a document in it by holding down a mouse button and then “drag” it into another folder and drop it there. The behaviour isn’t meant to be too realistic: for example, if you accidentally release the mouse button you don’t want the file to fall to the bottom of the screen; instead, it snaps back into the folder you dragged it from.

What isn’t so obvious is that computing has always been metaphor-driven, except for its very earliest days when programmers entered code and data by flipping switches on a front panel to define binary numbers. When you type the letter “A” on a keyboard, even on a pre-GUI operating system, the character that appears on the screen actually stands for two totally different things simultaneously – a 2D grid of numbers describing the glyph (that is, letter form) A stored somewhere in the screen driver, and the number 65 (binary 1000001), which is the ANSI code for A, somewhere in data memory where the text is being stored. Metaphor on metaphor.

A metaphor is indispensible when presenting data: a bar chart is a sequence of metaphors in which blocks of colour stand in for the numbers being represented. Choosing good metaphors for your data is so demanding that books have been written about it, most notably Edward Tufte’s superb trilogy starting with The Visual Display of Quantitative Information. But metaphor is just as important to the working of the human mind as it is to computing, and the two phenomena are closely related. You were probably taught in school, as I was, that metaphor is a “figure of speech”, a kind of ornament you employ occasionally to sound more interesting, and which you must never, ever mix. It’s actually far more than that, indeed one of the most important structuring elements of thought.

In 1980, two US philosophers, George Lakoff and Mark Johnson (L&J for short), wrote the influential book Metaphors We Live By, in which they explore the way most of our everyday language is metaphorical, and that the metaphors it employs are physical ones connected to the fact we have bodies that move in space and experience the force of gravity. One of the most common metaphorical structures is what L&J call More Is Up: whenever we describe something that’s increasing, we tend to use metaphors connected with upward motion, as in “house prices are on the rise again”, or “road accidents jumped by 23%”. The reason for the prevalence of this metaphor isn’t hard to analyse, because in the physical world when you pour water into a bucket, as you add more the level rises. It’s a natural feature of existence in a world with gravity. I’ve already given an example of More Is Up when I mentioned bar charts: typical graphs show an increase on the Y axis going upward, and to have it going downward (except for negative quantities) would be most counter-intuitive.

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