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All the parts of Extension are Extension; and all the parts of Duration, are Duration.       §9. There is one thing more, wherein Space and Duration have a
great Conformity, and that is, though they are justly reckoned
amongst our simple Ideas: Yet none of the distinct Ideas we have of
either is without all manner of Composition, it is the very nature of
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both of them to consist of Parts: But their Parts being all of the
same kind, and without the mixture of any other Idea, hinder them
not from having a Place amongst simple Ideas. Could the Mind, as
in Number, come to so small a part of Extension or Duration, as
excluded Divisibility, that would be, as it were, the indivisible
Unite, or Idea; by repetition of which, it would make its more
inlarged Ideas of Extension and Duration. But since the Mind is not
able to frame an Idea of any Space, without Parts; instead thereof it
makes use of the common Measures, which by familiar use, in each
Country, have imprinted themselves on the Memory (as Inches, and
Feet; or Cubits, and Parasangs; and so Seconds, Minutes, Hours,
Days, and Years in Duration:) The Mind makes use, I say, of such
Ideas as these, as simple ones: and these are the component Parts of
larger Ideas, which the Mind, upon Occasion, makes by the addition
of such known Lengths, which it is acquainted with. On the other
side, the ordinary smallest measure we have of either, is look’d on as
an Unite in Number, when the Mind by division would reduce them
into less Fractions. Though on both sides, both in addition and
division, either of Space or Duration, when the Idea under Consider-
ation becomes very big, or very small, its precise Bulk becomes very
obscure and confused; and it is the Number of its repeated additions,
or divisions, that alone remains clear and distinct, as will easily
appear to any one, who will let his Thoughts loose in the vast
Expansion of Space, or Divisibility of Matter. Every part of Dura-
tion is Duration too; and every part of Extension is Extension, both
of them capable of addition or division in infinitum. But the least
Portions of either of them, whereof we have clear and distinct Ideas,
may perhaps be fittest to be considered by us, as the simple Ideas of
that kind, out of which our complex modes of Space, Extension, and
Duration, are made up, and into which they can again be distinctly
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resolved. Such a small part in Duration, may be called a Moment,
and is the time of one Idea in our Minds, in the train of their
ordinary Succession there. The other, wanting a proper Name, I
know not whether I may be allowed to call a sensible Point, meaning
thereby the least Particle of Matter or Space we can discern, which
is ordinarily about a Minute, and to the sharpest eyes seldom less
than thirty Seconds of a Circle, whereof the Eye is the centre.
Locke Hum II, 15, §9, pp. 201-202-203