- 3.311
-
An expression presupposes the forms of all
propositions in which it can occur. it is the common
characteristic mark of a class of propositions.
- 3.312
-
It is therefore represented by the general form of
the propositions which it characterizes.
And in this form the expression is constant and
everything else variable.
- 3.313
-
An expression is thus presented by a variable,
whose values are the propositions which contain the expression.
(In the limiting case the variable becomes constant,
the expression a proposition.)
I call such a variable a "propositional variable".
- 3.314
-
An expression has meaning only in a proposition.
Every variable can be conceived as a propositional variable.
(Including the variable name.)
- 3.315
-
If we change a constituent part of a proposition
into a variable, there is a class of propositions which are all
the values of the resulting variable proposition. This class
in general still depends on what, by arbitrary agreement, we
mean by parts of that proposition. But if we change all those
signs, whose meaning was arbitrarily determined, into
variables, there always remains such a class. But this is now
no longer dependent on any agreement; it depends only on the
nature of the proposition. It corresponds to a logical form,
to a logical prototype.
- 3.316
-
What values the propositional variable can assume
is determined.
The determination of the values is the variable.
- 3.317
-
The determination of the values of the
propositional variable is done by indicating the
propositions whose common mark the variable is.
The determination is a description of these
propositions.
The determination will therefore deal only with symbols
not with their meaning.
And only this is essential to the determination,
that is is only a description of symbols and asserts nothing
about whiat is symbolized.
The way in which we describe the propositions is not
essential.
- 3.318
-
I conceive the proposition -- like Frege and
Russell -- as a function of the expressions contained in it.