In his Autobiography,John Stuart Mill,the 19th-century British political philosopher,portrayed his On Liberty as being "a kind of philosophic text-book" dedicated to a single truth,that is,"the importance,to man and society,of a large variety in types of character,and of giving full freedom to human nature to expand itself in innumerable and conflicting directions." The Mill of On Liberty may seem to be a pluralist who tends to prefer difference per se to goodness of a uniform pattern,many-sidedness to conformity,and eccentricity to mediocrity.This paper seeks to challenge this argument by paying close attention to the text.It argues that the Mill of On Liberty was far from a single-minded pluralist.Two divergent positions are found throughout his reasoning:one is a pluralist idea that an individual's own plan of life is the best,no matter how base or licentious it might be;the other is the belief that there exist a limited number of ideal ways of life which define what the good life is.The two positions are,if not mutually exclusive,at least in important aspects indicative of some profound tension at the center of Mill's thought.