Abstract

Three distinct things have been called "referential opacity," causing some confusion. A noun position in a sentence may be opaque in three different ways: (1) substitutivity of identity may fail there, (2) quantifiers prefixed to the sentence may not be able to bind variables in that position, or (3) substitutivity of identity may fail when the singular nouns in question are read as having small scope. Some connections among these three types of opacity are examined.