(This is intended as a comment on Thomas Forster’s point above, “i think there is a literature about them that goes back earlier than Quine,” but I’m over the character limit.)

Much earlier than Quine; Frege uses the trick in §10 of the Grundgesetze, setting (loosely, in modern terms) the True and False to their own singletons. He considers using the trick in greater generality, à la Quine, in footnote 17: “A natural suggestion is to generalize our stipulation so that every object is regarded as a course-of-values, viz., as the extension of a concept under which it and it alone falls.” I would be stunned if this did not influence Quine’s use, either directly or indirectly, subconsciously or consciously.

Heck discusses the stipulation is great detail in Part I of Reading Frege’s Grundgesetze, as part of his treatment of The Julius Caesar Problem, i.e., how can we be sure that the extension of some concept is not equal to Julius Caesar?

Personally, I feel that it is still too soon for Frege to worry about The Julius Caesar Problem. As he pointed out elsewhere, discussing a language that hasn’t yet been fully formalized is fraught with peril, and “Julius Caesar” is not yet a precisely-defined term in a formal language.  (Perhaps Caesar will end up being formalized as the extension of a concept after all—I don’t want to pre-judge the formalization of zoology.)  And obviously his proof of referentiality in §10 has to break down somewhere, or it would have been a consistency proof for naïve set theory.

(This is intended as a comment on Thomas Forster’s point above, “i think there is a literature about them that goes back earlier than Quine,” but I’m over the character limit.)

Much earlier than Quine; Frege uses the trick in §10 of the Grundgesetze, setting (loosely, in modern terms) the True and False to their own singletons. He considers using the trick in greater generality, à la Quine, in footnote 17: “A natural suggestion is to generalize our stipulation so that every object is regarded as a course-of-values, viz., as the extension of a concept under which it and it alone falls.” I would be stunned if this did not influence Quine’s use, either directly or indirectly, subconsciously or consciously.

Richard Heck discusses the stipulation is great detail in Part I of Reading Frege’s Grundgesetze, as part of his treatment of The Julius Caesar Problem, i.e., how can we be sure that the extension of some concept is not equal to Julius Caesar?

Personally, I feel that it is still too soon for Frege to worry about The Julius Caesar Problem. As he pointed out elsewhere, discussing a language that hasn’t yet been fully formalized is fraught with peril, and “Julius Caesar” is not yet a precisely-defined term in a formal language.  (Perhaps Caesar will end up being formalized as the extension of a concept after all—I don’t want to pre-judge the formalization of zoology.)  And obviously his proof of referentiality in §10 has to break down somewhere, or it would have been a consistency proof for naïve set theory.