Before a recent appointment with a physiotherapist, I picked up the July edition of that staple of waiting rooms and coffee tables, the National Geographic, and started leafing through it. I came across an article under the subject heading of "Science" on ways to slow down the human metabolism, which might, in the future, allow people to be put into suspended animation for space flight, or keep accident victims alive longer while awaiting transport to hospital. Although reasonably interested in the concepts described in the article, I was more interested in the tools used to communicate these concepts.

Analogies were drawn between the human body and an engine, and between oxygen and rocket fuel. Examples of squirrels hibernating and sharks surviving out of water were also cited, and one of the experiments done in the area was described with a large smattering of anecdotal detail – person, place, time etc. In all, I counted ten examples, two anecdotes and six analogies, in a piece that was 430 words long. This is equivalent to just over one page of a normally sized novel - in other words, a very short piece.

These tools are frequently used in National Geographic and on the Discovery channel, and they relate concepts to mental representations that are already familiar to the audience. The physiotherapist that I eventually got to see, compared the tendon in my upper thigh to a piece of rope and the muscle to which it was attached, to a spring. She also cited skiers and swimmers to exemplify the points made, and even related an anecdote about another patient who had come to her with a similar injury. In the same way as in the National Geographic, she was explaining abstract biological concepts by referring to things that were familiar to me.

Indeed, I have done the same thing myself in this article, when I said that 430 words was equivalent to just over one page of a novel. Even though the bare fact (430 words) was accurate, it wasn't meaningful to a normal reader, and the analogical transfer made it more so. But this introduces an interesting point about why writers and presenters often fail when they are communicating science. If I were writing this for a publisher, I would not have to explain what 430 words meant. Nor would I have to point out that 75,000 words is about the size of a short (250 page) novel. Because when you become familiar with material, then numbers, definitions, jargon and mathematical equations take on an implicit meaning in their own right, and no longer need to be related to anything else. In the same way, you would know if something was expensive simply by looking at the price tag, whereas this judgement wasn't so easy to make - without some kind of analogical mental translation - when the Euro first came into use, and the quantities didn't have an implicit meaning for you.

Presenters who are familiar with their own material, forget to make these connections, because everything they say is invested with meaning based on their experience. The analogies that acted as a kind of scaffolding when they first approached the subject, have long been dispensed with in a process that can best be paraphrased as: "forgetting what it was like not to know". It's not that the presenter can't make these connections, but rather that they don't see the need to. This is, I believe, the main reason why technical presentations fail.