gives _plus_, _because_ it could not give the same as _minus_ multiplied by _plus_, which gives _minus_. So, some ethical writers begin by assuming, that certain general sentiments are the _natural_ sentiments of mankind, and thence argue that any which differ are morbid and _unnatural_. Thus, lastly, Hobbes and Rousseau rested the existence of government and law on a supposed social compact, and not on men's perception of the interests of society, which, however, could be the only ground for their abiding by such compact if a fact. 3. In Ignoratio Elenchi, or, the Fallacy of Irrelevant Conclusion, the error lies not either in mistaking the import of the premisses, or in forgetting what they are, but in mistaking what is the conclusion to be proved. Sometimes, a particular is substituted for the universal as the proposition needing proof, and sometimes, a proposition with different terms. Under this fallacy come the cases, not only of proving what was not denied, but of disproving what was not asserted; e.g. the argument used against Malthus (whose own position was, that population increases only _in so far as not kept down_ by prudence, or by poverty and disease), that, at times, population has been nearly stationary; or again, that, in some country or other, population and comfort are increasing together, Malthus himself having asserted that this might be so, if capital has increased. Similarly, even Reid, Stewart, and Brown (not merely Dr. Johnson) urged that Berkeley ought, if consistent, to have run his head against a post, as though the non-recognition of an occult _cause_ of sensations implies disbelief in any _fixed order among them_. BOOK VI. ON THE LOGIC OF THE MORAL SCIENCES. CHAPTER I. INTRODUCTORY REMARKS. Many complex problems have been resolved through the use of the Scientific Methods, and thus only. The most complex of all problems are the problems relating to Man himself; and of them those concerned with the Mind and Society have never been scientifically resolved. They can be rescued from empiricism, if at all, only by being submitted to some of the methods already characterised as applicable to science in general. Which of these methods must be selected, and why; what are the causes of previous failures; and what degree of success now is possible or probable, will be considered in this book, when a preliminary objection (_based on the theory of free will_), that men's actions are not, like other natural events, subject to invariable laws, has been first removed. CHAPTER II. LIBERTY AND NECESSITY.