The gist of the Unicorn Argument against representational theories of consciousness is that while both higher-order and first-order representational theories (HORs and FORs) require the existence of such a property as being represented, there is no such property since we can mentally represent things that don’t exist and things that don’t exist don’t instantiate properties.
One way one might attempt to resist the premise that the non-existent instantiate no properties is in terms of a notion of truth in fiction. One might embrace the following pair of views:
(1) There literally is no such person as Sherlock Holmes and it is no more true of Holmes that he does coke than that he smokes pot.
(2) There is a sense of â€œtrueâ€ whereby it is more true of Holmes that he does coke than that he smokes pot.
One might hold that the â€œtruthsâ€ about Holmes in (2) hold in virtue of it being true in the literal sense, true in sense (1), that Sir Arthur Conan Doyle wrote stories about Holmes doing coke but not true in sense (1) that Doyle wrote stories about Holmes smoking pot. There is thus a sense, then, in which Holmes, in spite of not existing, instantiates properties.
Note, however, how little this will help HORs and FORs. Those theories need it to be true (in sense (1)) that there is such a property as being represented. HORs and SORs want to explain, among other things, what it means for a mental state that exists to be conscious. And their explanation will be one that includes, among other things, that it is true in sense (1), that the state in question is represented. Mutatis Mutandis for FORs and their explanations of being a phenomenal property in virtue of being a represented property.
However, when things are represented, it is infrequently true of them in sense (2) that they are represented. Consider Holmes again. While it is true (2) of Holmes that he does coke, since it is part of Doyleâ€™s story, it is not true (2) of Holmes that Doyle wrote a story about Holmes, since that is not part of the story. (I must confess to not having read many Sherlock Holmes stories, but Iâ€™m relatively confident in guessing that Doyle did not engage in the kind of self-referential meta-fiction that might constitute an exception to my claim.) Whatever sense might be made of the instantiation of properties by non-existents in terms of truth in fiction it is not going to be the kind needed to block the inference from “we represent things that do not exist” and “things that do not exist do not instantiate properties” to “there is no such property as being represented”.