Gertrude Stein once remarked that "to write is to live is to be."
Or not. Actually, Gertrude Stein never said any such thing. Or perhaps she did. When I say Gertrude Stein never said any such thing I really mean that I myself have no evidence that Gertrude Stein ever said any such thing. She certainly could have said such a thing. I know only a small fraction of the things Gertrude Stein ever said--a very small fraction: I've never actually read anything by Gertrude Stein; the extent of my knowledge of her writings extends scarcely further than "A rose is a rose is a rose." Which, when you think about it, makes only slightly more sense than my hypothetical remark above.
Gertrude Stein also wrote The Autobiography of Alice B. Toklas, and for all I know that book might contain a sentence espousing the equivalence of writing and living and being. I doubt it, but it's certainly possible. After all, Gertrude Stein presumably possessed a vocabulary that included all the words in my "quote," along with the linguistic ability to arrange those words in that same syntactical order. Maybe I'm wrong about her vocabulary. She does not seem to have known, for example, what the word "autobiography" means.
The question, then, is this: If Gertrude Stein did, in fact, write a sentence that I assumed she did not write--that I presented merely as a way to add (fraudulent) gravitas to this post--then would what I did nevertheless be considered quotation? And had I made the statement without stating that Gertrude Stein made the statement that I assumed she had not made, would my statement then be exhibit A in a case of plagiarism that would no doubt have amused Gertrude Stein immensely. If she were into that sort of thing. I don't know. As I say, I've never read anything by Gertrude Stein. I have no idea what would have amused her.