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48

In order to put this into a shape capable more explicit shape,
I will first call your attention to a corollary from it.
A corollary to a proposition of Euclid is a
necessary consequence drawn from it by some
editor of Euclid's Elements and inserted by him, originally,
I suppose, marked with a little crown in the margin. These
additions are, for the most part, trifles propositions that Euclid thought
not worth too obvious for special notice. Hence, any easily drawn necessary
consequence of a proposition is termed a corollary.
Here I will tell you a secret about necessary consequences.
It is a very useful thing to know, although
most logicians are quite entirely ignorant of it. It is that
not even this simplest necessary consequence can be
drawn except by the aid of Observation, namely the
observation of some feature of something of the