premise: Writing Degree Zero (French: "Le degré zéro de l'écriture" ) is a book of literary criticism by Roland Barthes. First published in 1953, it was Barthes' first full-length book and was intended, as Barthes writes in the introduction, as "no more than an Introduction to what a History of Writing might be."
hypothesis: Writing Degree Zero was the first piece of literary criticism Barthes wrote. 
reason: It said it was his first full length book, but it didn't say whether it was the first PIECE of literary criticism he wrote. Maybe he wrote an article somewhere else or a novella. There is no way to know.