Decision rationale: The why and the wherefore

By Gordon Rugg

People are usually able to give you reasons for the things that they do. Sometimes those reasons make perfect sense; sometimes they make sense once you understand the background; other times, you’re left wondering what one earth is going on in the person’s head. There’s also the issue of whether those reasons bear any relation to reality, but that’s another story.

This article is about how one apparently pointless superstition can be traced back to a perfectly sensible piece of evidence-based reasoning that subsequently spiralled off into a very different direction. It involves the ancient Roman practice of examining the livers of sacrificed sheep and poultry as a way of predicting the future.

So what does this practice have to tell us about how people make decisions today? Actually, quite a lot. It’s a good illustration of some fundamental points that are as important now as they were over two thousand years ago, when this bronze model of a liver was created to help Roman fortune tellers assess the omens before a major decision.


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Why heavy things are heavy: Brought to you by classical logic

By Gordon Rugg

Here’s Vitruvius again, trying to explain something using the four elements theory again, and ending up with a distinctly dodgy chain of reasoning again. You get the feeling that his heart isn’t really in it, and that he knows he’s working with tools that just aren’t up to the job.

6. To begin with fir: it contains a great deal of air and fire with very little moisture and the earthy, so that, as its natural properties are of the lighter class, it is not heavy.

I know how he must have felt. When I started to add tags to this post, the software helpfully suggested adding the tags Brookside characters and mattress. Is there a Brookside character named Vitruvius Mattress? I really don’t want to know.

Why birds can fly: Brought to you by classical logic

By Gordon Rugg

You might already be familiar with the Monty Python scene where one of King Arthur’s knights uses logical reasoning to show why witches and ducks float. As with much of Monty Python, it’s fairly close to something that actually happened.

Here’s Vitruvius, the famous Roman engineer and architect, using the four elements theory (that all things are made of various mixtures of air, fire, water and earth) to explain why birds are able to fly.

Winged creatures have less of the earthy, less moisture, heat in moderation, air in large amount. Being made up, therefore, of the lighter elements, they can more readily soar away into the air.

(From his Ten Books on Architecture)

Disclaimer: If you try using this quote as justification for throwing an alleged witch into a pond, then you’re on your own – this post is tagged under “error”…