During his final years, John Stuart Mill reportedly attempted to update the argument of On Liberty (1859). Published posthumously in 1907, ‘On Social Freedom’ represents the initial, unrefined draft of his reworked ideas. This article argues that John Stuart Mill was not the author of ‘On Social Freedom’. First, we revisit the question of the essay’s authorship traditionally: the emphasis is on the essay’s content and the historical context of the mid-twentieth-century debate on Mill as its author. We trace the disagreement to two broad reactions to Mill’s thought. Ultimately, the question of whether the manuscript’s substantial divergence from J. S. Mill’s renowned works is enough to refute his authorship depends on one’s interpretation of Mill as a systematic philosopher. Second, we tackle this task non-traditionally: the focus shifts to the tools of computer-assisted authorship identification and the use of machine learning (ML) techniques. Once we establish some key ideas, methods, and limitations of this field of studies, we present our attempts at a computer-assisted solution to the puzzle. The results of our experiments, using ML techniques, corroborate the conclusions reached via the traditional route.