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And by first, I mean principles akin to the conclusion, for

principle means the same as first And the principle or first step

in demonstration is a proposition incapable of syllogistic proof,

i.e. one to which there is none prior. Now of such syllogistic

principles I call that a θέσις which you cannot demonstrate, and

which is unnecessary with a view to learning something else. That

which is necessary in order to learn something else is an Axiom.