 In a recent article, Christoph Schmidt-Petri, Michael Schefczyk, and Lily Osburg (2022) employ stylometric techniques to ascertain Taylor Mill’s role in composing On Liberty. This innovative approach presupposes that authors have stylistic “fingerprints” that can be identified via machine learning algorithms, so that by comparing a text whose author is unknown to others known to have been written by different “suspects” (that is, potential authors) the former’s author can be identified. Their conclusion is that several passages of On Liberty were written not by Mill alone but by either Taylor Mill or the two of them jointly. One limitation of their method is that we cannot be any more confident about their conclusions than we are about their ascriptions of the texts that serve as inputs to the algorithms. As they acknowledge, there is no consensus about some of these. For instance, they assume not only that the chapter of the Principles on the future of the working class was written exclusively by Taylor Mill but that the remainder of the two-volume work was written jointly—even the most “purely scientific” portions. As with the Principles of Political Economy, then, the evidence regarding Taylor Mill’s claim to be regarded as the co-author of On Liberty is equivocal.