We all have myths through which we explain the world. The very word "myth", however, is a little awkward, because it is sometimes used simply to mean "false", but its other meaning can be very useful. I also talk about dreams and dramas and visions and so forth. Whichever way one talks about it, it's about an imaginative background, a way of seeing a problem in the world which determines what questions you ask and how you select your questions.

The idea that all you need to do is simply and honestly find the answers to questions does not work. You've got to have the right questions. As the history of science has built up and developed, at every stage this has been a very important factor.

In the 17th century the imagery of clockwork was terribly strong, so when Newton was trying to understand the universe he was seeing it as a clock heading in a single direction. It's not surprising that people were terribly impressed with clockwork because at the time it was magic, a miracle, a mystery. Once you have established a way like that of thinking about how things work, you stick with it, it is gratifying and satisfying – you find you can apply it to lots and lots of things, so you don't feel a need to look for another one.

It remains, of course, with us. We still talk about a mechanism. And the idea that all the bits of our bodies are machines is a thought often used today. For one thing it makes our bodies less frightening – a machine is something that people make, something that people can control, can take out and alter. It provides a sense of control.

People very much liked to look at things this way. After a time, however, physics began to find the machine image not very satisfactory, so from Michael Faraday’s time, instead of little particles you started having fields and waves and so on. Different imagery was required. Then from Albert Einstein on, the imagery questions became very difficult indeed – there is no comprehensive model or pattern which you can imaginatively see.

By the 19th century, the age of Charles Darwin, the market had already begun to be an image that fascinated people. The way in which Herbert Spencer developed Darwin’s ideas to create this terrible idea of “social Darwinism” was an attempt to make a direct equation between the processes of the market and the processes of nature. On the one hand you see the idea of the market deployed to understand nature, illustrating “the survival of the fittest” with reference to the stock exchange; on the other you see the idea flipped so that it can be said, “the stock exchange is actually just a jungle.” On both sides of the coin, things are simplified.

Why have the crude, brutalist images of social Darwinism have been so persistent? Because they have that enormous flexibility. They can be used both ways. If people are morally worried about what’s happening on the stock exchange, they can shift that worry by saying, “It’s just nature, isn’t it?” On the other hand, if they are worried about what’s going on in the jungle, they can say, “It’s all a great machine.” You are getting away from agency all the time.

These images, both of which have been very powerful in science, as well as everywhere else, have an appeal because they simplify things. But they simplify them in a way which gets rid of certain awkward frictions. And it is hard to debunk this pattern because it’s doing so much for people; soothing their anxieties – making them think it’s all quite simple.

Marxism was a big feature of the time when I was growing up, so it’s the political philosophy I'm most familiar with. It is another striking example of an imaginative system – a fable, a dream, a drama, a vision – within which a lot can go forward. Of course, there was a good deal of fairly dodgy stuff on the fringe of science which was Marxist, but I don’t think it was any dodgier than the monetarist things that have been going on since then. The mythology of how markets work, of how money can do things on its own, is as remote from solid physical reality as these other things. And of course, whatever the mythology of the time is, those inside it don’t recognise it as such. They think they are just noticing facts.

Mary Midgley is a moral philosopher and author of Beast And Man: The Roots of Human Nature. This article is excerpted from the latest Theos report, Discussing Darwin and first appeared in The Guardian on 15 August 2009.