The two next chapters of Mr Mill, noticing some other minor peculiarities (all of them unfortunate, and one, p. 447, really unaccountable) of Sir W. Hamilton's Formal Logic; and some Fallacious Modes of Thought countenanced by Sir W. Hamilton (chs. xxiii., xxiv.--pp. 446, 478), we are compelled to pass over. We must find space, however, for a few words on the Freedom of the Will (ch. xxv.), which (in Mr Mill's language, pp. 488--549), 'was so fundamental with Sir W. Hamilton, that it may be regarded as the central idea of his system--the determining cause of most of his philosophical opinions.' Prior to Sir W. Hamilton, we find some writers who maintain the doctrine of Free-will, others who maintain that of Necessity: each supporting their respective conclusions by reasons which they deem sufficient. Sir W. Hamilton declares that both the one doctrine and the other are inconceivable and incomprehensible; yet that, by the law of Excluded Middle, one or other of them must be true: and he decides in favour of Free-will, of which he believes himself to be distinctly conscious; moreover, Free-will is essential (he thinks) to moral responsibility, of which also he feels himself conscious. He confesses himself, however, unable to explain the possibility of Free-will; but he maintains that the same may be said about Necessity also. 'The champions of both the two opposite doctrines are at once resistless in attack, and impotent in defence'--(Hamilton's 'Footnotes on Reid,' p. 602.) Mr Mansel also asserts, even more confidently than Sir W. Hamilton, that we are directly conscious of Free-will--(p. 503). Sir W. Hamilton has himself given some of the best arguments against the doctrine of Free-will, in refutation of Reid: arguments, some of which are here cited by Mr Mill with praise which they well deserve--(pp. 497, 498). But Mr Mill's own reasoning on the same side is of a still higher order, enlarging the grounds previously urged in the last book of his 'System of Logic,' He protests against the term _Necessity_; and discards the idea of Necessity, if it be understood to imply anything more than invariability of antecedence and consequence. If it mean _that_, experience proves thus much about antecedents in the world of mind, as in the world of matter: if it mean more, experience does not prove more, either in the world of matter or in the world of mind: nor have we any grounds for affirming it in either--(p. 501.) If it were true, therefore, that consciousness attested Free-will, we should find the testimony of consciousness opposed to a full proof from experience and induction. But does consciousness really attest what is called Free-will? Mr Mill analyzes the case, and declares in the negative.