The English works of Thomas Hobbes of Malmesbury, Volume 07 (of 11)
Thomas Hobbes · en
Lastly, you object “that motion is accidentary to a point, and
consequently not essential, nor to be put into the definition.” And is
not the circumduction of a semicircle accidentary to a sphere? Or do you
think the sphere of the sun was generated by the revolution of a
semicircle? And yet it was thought no fault in Euclid to put the motion
into the definition of a sphere.
The conceit you have concerning definitions, that they must explicate
the essence of the thing defined, and must consist of a _genus_ and a
_difference_, is not so universally true as you are made believe, or
else there be very many insufficient definitions that pass for good with
you in Euclid. You are much deceived if you think these woful notions of
yours, and the language that doth everywhere accompany them, show
handsomely together. Or that such grounds as these be able to sustain so
many, and so haughty reproaches as you advance upon them, so as they
fall not, as you shall see immediately, upon your own head. I say a
point hath quantity, but not to be reckoned in demonstrating the
properties of lines, solids, or superficies; you say it hath no quantity
at all, but is plainly nothing.
The first of the petitions of Euclid is, “that a line may be drawn from
point to point at any distance.” The second, “that a straight line may
be produced.” The third, “that on any centre a circle may be described
at any distance.” And the eighth axiom (which Sir H. Savile observes to
be the foundation of all geometry) is this, “_Quæ sibi mutuo congruunt,
etc._ Those things that are applied to one another in all points are
equal.” All or any of these principles being taken away, there is not in
Euclid one proposition demonstrated or demonstrable. If a point have no
quantity, a line can have no latitude; and because a line is not drawn
but by motion, by motion of a body, and body imprinteth latitude all the
way, it is impossible to draw or produce a straight line, or to describe
a circular line without latitude. Also if a line have no latitude, one
straight line cannot be applied to another. To them therefore that deny
a point to have quantity, that is, a line to have latitude, the
forenamed principles are not possible, and consequently no proposition
in geometry is demonstrated or demonstrable. You therefore that deny a
point to have quantity, and a line to have breadth, have nothing at all
of the science of geometry. The practice you may have, but so hath any
man that hath learned the bare propositions by heart; but they are not
fit to be professors either of geometry or of any other science that
dependeth on it. Some man perhaps may say that this controversy is not
much worth, and that we both mean the same thing. But that man, though
in other things prudent enough, knoweth little of science and
demonstration. For definitions are not only used to give us the notions
of those things whose appellations are defined, for many times they that