has different modes of signification--and so belongs to different symbols--
or that two words that have different modes of signification are employed
in propositions in what is superficially the same way. Thus the word 'is'
figures as the copula, as a sign for identity, and as an expression for
existence; 'exist' figures as an intransitive verb like 'go', and
'identical' as an adjective; we speak of something, but also of something's
happening. (In the proposition, 'Green is green'--where the first word is
the proper name of a person and the last an adjective--these words do not
merely have different meanings: they are different symbols.)


3.324 In this way the most fundamental confusions are easily produced (the
whole of philosophy is full of them).


3.325 In order to avoid such errors we must make use of a sign-language
that excludes them by not using the same sign for different symbols and by
not using in a superficially similar way signs that have different modes of
signification: that is to say, a sign-language that is governed by logical
grammar--by logical syntax. (The conceptual notation of Frege and Russell
is such a language, though, it is true, it fails to exclude all mistakes.)


3.326 In order to recognize a symbol by its sign we must observe how it is
used with a sense.


3.327 A sign does not determine a logical form unless it is taken together
with its logico-syntactical employment.