Two years ago, I ran a survey of semantic intuitions concerning empty names, that is, names that appear to be without a referent (e.g., ‘Santa Claus’, ‘Superman’). Some of those who kindly participated in the survey asked me to post the results of the survey. (Thanks again for your help, folks.)
The question was whether sentences and pseudo-sentences such as ‘Santa Claus is fat’, ‘Santa Claus doesn’t exist’, and ‘#^*g~)# doesn’t exist’ are true, false, or have no truth value. I found the results quite interesting. Very briefly, (1) most people have no difficulty assigning truth values to most sentences containing empty names or words that look like empty names, but (2) they balk at assigning truth values to sentences that contain non-words in the place of an empty name. However, (3) different people disagree on which sentences have truth values and in some cases, on which truth values certain sentences have.
I think these results (in combination with some other considerations) cause trouble for Millian theories of proper names. here, Mind and Language has recently published an entire issue on proper names.