I was in a café in a garden centre in Sussex recently when I ordered a coffee which was advertised as ‘medium’.
This suited me as ‘medium’ was the middle of three options and the name suggested it was neither small, nor large. It must lie somewhere in between, and therefore be of a moderate size.
The ‘medium’ was, in fact, a large size by anyone’s estimation, accepting the point that size is a relative concept. And I was paying for all that extra coffee.
Therefore, and presumably, the ‘small’ must have been of a medium size. And by rights, the ‘large’ must have been massive – plant pot size – and being a garden centre this may have been a sensible arrangement.
Unfortunately, I had fallen prey to a rhetorical fallacy, known as argumentum ad temperantium. It sounds a bit like a Harry Potter spell, but actually means ‘argument to moderation’ or ‘false compromise’, among other names.
When presented with a choice of three options, two of which appear to be extremes, the middle path seems the most reasonable one to take. I wanted a medium size coffee but ended up buying a large coffee because it was the middle of three options.
This device has been used since antiquity and is still being used widely by communicators and coffee purveyors alike.