Editing Extension (semantics) (section)

== Metaphysical implications ==

There is an ongoing controversy in [[metaphysics]] about whether or not there are, in addition to actual, existing things, non-actual or nonexistent things.  If there are—if, for instance, there are possible but non-actual dogs (dogs of some non-actual but possible species, perhaps) or nonexistent beings (like Sherlock Holmes, perhaps)—then these things might also figure in the extensions of various concepts and expressions.  If not, only existing, actual things can be in the extension of a concept or expression.  Note that "actual" may not mean the same as "existing".  Perhaps there exist things that are merely possible, but not actual.  (Maybe they exist in other universes, and these universes are other "[[possible worlds]]"—possible alternatives to the actual world.)  Perhaps some actual things are nonexistent.  (Sherlock Holmes seems to be an ''actual'' example of a fictional character; one might think there are many other characters [[Arthur Conan Doyle]] ''might'' have invented, though he actually invented Holmes.)

A similar problem arises for objects that no longer exist.  The extension of the term "Socrates", for example, seems to be a (currently) non-existent object.  [[Free logic]] is one attempt to avoid some of these problems.