n a propositional element signifies a
complex, this can be seen from an indeterminateness in the propositions
in which it occurs. In such cases we know that the proposition leaves
something undetermined. (In fact the notation for generality contains
a prototype.) The contraction of a symbol for a complex into a simple
symbol can be expressed in a definition.

3.25 A proposition cannot be dissected any further by means of a
definition: it is a primitive sign.

3.261 Every sign that has a definition signifies via the signs that
serve to define it; and the definitions point the way. Two signs cannot
signify in the same manner if one is primitive and the other is defined
by means of primitive signs. Names cannot be anatomized by means of
definitions. (Nor can any sign that has a meaning independently and on
its own.)

3.262 What signs fail to express, their application shows. What signs
slur over, their application says clearly.

3.263 The meanings of primitive signs can be explained by means of
elucidations. Elucidations are propositions that stood if the meanings
of those signs are already known.

3.3 Only propositions have sense; only in the nexus of a proposition
does a name have meaning.

3.31 I call any part of a proposition that characterizes its sense
an expression (or a symbol). (A proposition is itself an expression.)
Everything essential to their sense that propositions can have in common
with one another is an expression. An expression is the mark of a form
and a content.

3.311 An expression presupposes the forms of all the propositions in
which it can occur. It is the common characteristic mark of a class of
propositions.

3.312 It is therefore presented by means of the general form of the
propositions that it characterizes. In fact, in this form the expression
will be constant and everything else variable.

3.313 Thus an expression is presented by means of a variable whose
values are the propositions that contain the expression. (In the
limiting case the variable becomes a constant, the expression becomes a
proposition.) I call such a variable a 'propositional variable'.

3.314 An expression has meaning only in a proposition. All variables can
be construed as propositional variables. (Even variable names.)

3.315 If we turn a constituent of a proposition into a variable, there
is a class of propositions all of which are values of the resulting
variable proposition. In gener