the preface. As far as I can recollect, it was entirely written by him.
The 1818 edition of Frankenstein was published anonymously, and early readers and reviewers often attributed it to Percy Shelley, not Mary. According to Mary in 1831 (and subsequent scholarship), Percy did largely write the 1818 "Preface," and it is now estimated by Charles Robinson that Percy contributed between 4000 and 5000 words to Mary's 72,000 word manuscript. See Robinson, ed., The Original Frankenstein; or, the Modern Prometheus, by Mary Shelley (with Percy Shelley) [New York: VIntage Classics, 2009].