Symbolic Logic
by Lewis Carroll
“Book 6: Chapter 1”
Additional Information
 Year Published: 1896
 Language: English
 Country of Origin: United States of America
 Source: Carroll, L. (1896). Symbolic Logic. New York; Macmillan & Co.

Readability:
 Flesch–Kincaid Level: 10.5
 Word Count: 257
 Genre: Informational
 Keywords: math history, mathematics
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BOOK VI.
THE METHOD OF SUBSCRIPTS.
CHAPTER I.
INTRODUCTORY.
Let us agree that “x1” shall mean “Some existing Things have the Attribute x”, i.e. (more briefly) “Some x exist”; also that “xy1” shall mean “Some xy exist”, and so on. Such a Proposition may be called an ‘Entity.’
[Note that, when there are two letters in the expression, it does not in the least matter which stands first: “xy1” and “yx1” mean exactly the same.]
Also that “x0” shall mean “No existing Things have the Attribute x”. i.e. (more briefly) “No x exist”; also that “xy0” shall mean “No xy exist”, and so on. Such a Proposition may be called a ‘Nullity’.
Also that ”Ü” shall mean “and”.
[Thus “ab1 Ü cd0” means “Some ab exist and no cd exist”.]
Also that ”∂” shall mean “would, if true, prove”.
[Thus, “x0 ∂ xy0” means “The Proposition ‘No x exist’ would, if true, prove Proposition ‘No xy exist’”.]
When two letters are both of them accented, or both not accented, they are said to have ‘Like Signs’, or to be ‘Like’: when one is accented, and the other not, they are said to have ‘Unlike Signs’, or to be ‘Unlike’.