troublesome words
some words (used in my introduction) seem to be particularly troublesome. they lend themselves to being taken in the wrong way. this shouldn't be a surprise, because I'm pretty sure they caused me trouble too, back in the day
the number one culprit is Descartes' word extension. How could old René have made 'extension' the key to a good half of the world (the solid material part as opposed to the airy mental part)? isn't extension something that you have to apply to the planning authority for permission to do? even if we steer clear of bricks and mortar, isn't extension the act of stretching something, be it in time or space?
apparently not. extension seems to be the mere fact of something having been stretched out over an 'extent'. and maybe no act of stretching was involved, maybe the something just has and always had a certain extent
res extensa (Latin for 'extended stuff') is the stuff of the material world, according to Descartes. its defining property is that it takes up a certain amount of space, that it has extent
I mentioned time a few sentences back. that was a red herring. res extensa is extended in space, but not time. Henri Bergson (much later: 1890 vs 1630) was the one who started making a fuss about extension in time: he called it durée (duration)
another troublesome word -- elastic. elastic bands have two properties: 1 they are stretchy, you can stretch them; 2 they pull back. by stretching an elastic band you engender an opposing force. the elastic band wants to return to its original length. are you in any doubt about that? surely you feel the force of the elastic band's desire in your fingers?
my guinea-pig tends to think in terms of the first property, the fact of being stretchable. but in physics it is the second property, the force arising out of the stretching, that is important. (although it must be granted that the second property would not exist without the first!)
I find that the word elastic comes from the Greek elauno I drive or set in motion. Which makes me think of toy aeroplanes made of balsa wood, with propellers powered by elastic bands, twisted up before launch. yes, elastic bands can do driving.