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Thirdly, Σημειωτική.
      §4. Thirdly The Third Branch may be called σημειωτική, or the
Doctrine of Signs, the most usual whereof being Words, it is aptly
enough termed also λογική, Logick; the business whereof, is to con-
sider the Nature of Signs, the Mind makes use of for the under-
standing of Things, or conveying its Knowledge to others. For
since the Things, the Mind contemplates, are none of them, besides
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it self, present to the Understanding, ’tis necessary that something
else, as a Sign or Representation of the thing it considers, should be
present to it: And these are Ideas. And because the Scene of Ideas
that makes one Man’s Thoughts, cannot be laid open to the im-
mediate view of another, nor laid up any where but in the Memory,
a no very sure Repository: Therefore to communicate our Thoughts
to one another as well as record them for our own use, Signs of our
Ideas are also necessary. Those which Men have found most con-
venient, and therefore generally make use of, are articulate Sounds.
The Consideration then of Ideas and Words, as the great Instruments
of Knowledge, makes no despicable part of their Contemplation,
who would take a view of humane Knowledge in the whole Extent
of it. And, perhaps, if they were distinctly weighed, and duly con-
sidered, they would afford us another sort of Logick and Critick,
than what we have been hitherto acquainted with.
Locke Hum IV, 21, §4, pp. 720-721