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September 29, 2012


"The two formulae agree everywhere, but so do the competing definitions of a circle on the one hand as "a figure in which all the lines drawn from the center to the circumference are equal to each other" and on the other as "a plane figure described by a line of which one end is fixed while the other is moveable", which is evidently something of moment, since only the second "is adequate and … expresses the efficient cause" (p 95)."

The passage on p.95 brought me up short when reading it, because I can't figure out what is wrong with the "inadequate" definition of a circle. I *think* he is using an example of Spinoza's there, but he doesn't cite him if he is. (If he's not using Spinoza's example, then I find it even more confusing: What the hell is "the efficient cause of a circle" supposed to mean, if Förster is speaking in his own voice in that passage?)

It reads very much as if it's a Spinozan example, so much so that I just assumed it was, but now I see you're right, it isn't explicitly attributed to him (and it comes up again on p 252 where again it isn't explicitly attributed to him). But at least the language of efficient causes is from Spinoza (note 3 on p 253), as, apparently, is the use of mathematical examples—it's just not clear that this mathematical example is from Spinoza.

I just assumed, at that passage on p 95, that it was indeed true that starting from the first definition of a circle you can't deduce all the properties of a circle, but it would have been nice if some specific property whose deduction the second definition does enable but the first doesn't had been given.

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