This log was inspired by "How to Read Wittgenstein" and "Ludwig Wittgenstein: the duty of genius" by Ray Monk. It is based on reading Tractatus Logico-Philosophicus by Ludwig Wittgenstein translated by D. F. Pears & B. F. McGuinness (Routledge and Kegan Paul:1963)

Tuesday, April 1, 2008

Truth Value Tables and Propositions.

The truth values of elemental propositions denote the possibility that matters of fact may be the case or not. We can exhibit these in tables that can easily be understood. Each column is dedicated to an elemental proposition listed in the heading followed by as many truth values as needed. ('T' means 'true', 'F' means 'false'.) The truth table for a single elemental proposition has two rows and the number of rows in the table is doubled for each additional elemental proposition.

p
=
T
F

p q
===
T T
F T
T F
F F

p q r
====
T T T
F T T
T F T
F F T
T T F
F T F
T F F
F F F

A proposition expresses both agreement and disagreement with the truth values of elemental propositions. This makes those truth values the conditions that determine whether the proposition is true or not.

It immediately strikes one that introducing elemental propositions provided the vasis for understanding all other kinds of sentences. Indeed, elemental propositions are palpably required to understand general propositions.

Given n elemental propositions, we can calculate the L(n) ways a particular proposition can both agree and disagree with their truth values. In an additional column dedicated to that proposition, we can denote that the proposition agrees with the combination of values in that row of the truth table by assigning the mark 'T' to the row. The absence of this mark denotes disagreement.

Now, expressing agreement with the truth values of the elemental propositions expresses the truth values of the proposition itself. Thus, the proposition is the expression of its truth values. The sign that results from adding the correlating marks to the truth table is its propositional sign.

It is clear that the complex of signs 'F' and 'T' in the truth table has no object (or complex of objects) corresponding to it, just as there is none corresponding to the horizontal and vertical lines or to the brackets. There are no 'logical objects'. Of course the same applies to all signs that express what truth tables express.

For example:
(p q
T T T
F T T
T F
F F T)
is a propositional sign.

If the order of the truth table is fixed once and for all by a combinatory rule, then the last column by itself will express the truth-conditions. If we now write this column as a row, the propositional sign will become
'(TT-T) (p,q)' or more clearly '(TTFT) (p,q)'.
(Note that the number of places in the left-hand pair of brackets is determined by the number of terms in the right-hand pair.)

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