they react differently when they realize what they've done in each case. I'm going to give you two conversations. In each conversation there are two characters, A and B, plus one outsider. In the first conversation speaker B plays the devil's advocate; you're supposed to fired speaker A's reactions normal.
A. "The man in the doorway over there looks pretty silly." Outsider: "But there is no man in the doorway over there." A. (Looks again) "Oh! I thought there was; I was wrong." B. "Does he look anything like your department chairman?" A. "Who?" B. "The man in the doorway over there." A. "There isn't any man there; I was mistaken about that." B. "Well, he doesn't exist, but he's there, isn't he?" A. "Look, I was talking about a guy who exists; that is I thought I was,but I was wrong, I wasn't talking about anybody. I can't tell you what "he" looks like because there's no "he" to describe."
Now that was supposed to be a case of failure of reference. The speaker was trying to refer to someone, but he just made a mistake and failed to do so. When confronted with questions about the object he was referring to he treats the questions as spurious (i.e., he does this once he realizes his mistake). Now here's another case:
A. "The unicorn I dreamed about last night looked pretty silly." Outsider: "But there are no unicorns." A. "So what?" Outsider: "Well there aren't any unicorns, so there couldn't be any such thing as the unicorn you dreamed about last night, so "it" couldn't possibly have looked silly." A. "Come on, it's not a real unicorn, it's one I dreamed about." B. "Did it look anything like your department chairman?" A. "No, actually it looked a little bit like my hairdresser."
In this conversation speaker A rejects the contention that he had failed to refer to anything, though he grants that what he is referring to doesn't exist. And he treats questions about it as perfectly reasonable. Some philosophers would criticize A for this; they'll say that he should have rejected the