Editing Propositional attitude (section)

===Indiscernibility of identicals===
{{see|Use–mention distinction}}
<blockquote>
One of the fundamental principles governing identity is that of substitutivity{{Clarify|date=July 2011}}, also known as fungibility&nbsp;— or, as it might well be called, that of ''[[Salva veritate|indiscernibility of identicals]]''.  It provides that, ''given a true statement of identity, one of its two terms may be substituted for the other in any true statement and the result will be true''. It is easy to find cases contrary to this principle. For example, the statements:

:(1) Giorgione = Barbarelli,
:(2) Giorgione was so called because of his size.
are true;  however, replacement of the name ''Giorgione'' by the name ''Barbarelli'' turns (2) into the falsehood:
:(3) Barbarelli was so called because of his size.<ref>[[Willard Van Orman Quine|W. V. O. Quine]], ''Quintessence, extensions, Reference and Modality'', p. 361</ref>
</blockquote>

Quine's example here refers to [[Giorgio Barbarelli]]'s [[sobriquet]] "Giorgione", an Italian name roughly glossed as "Big George." The basis of the paradox here is that while the two names signify the same individual (the meaning of the first statement), the names are not themselves identical; the second statement refers to an attribute (origin) that they do not share.<ref group="upper-alpha">See "[[Who's on First?]]."</ref>