All reflecting men acknowledge that both the theory and the practice of morality have advanced with the general advance in the intelligence and civilisation of the human race. But, if this be so, morality must be a matter capable of being reasoned about, a subject of investigation and of teaching, in which the less intelligent members of a community have always something to learn from the more intelligent, and the more intelligent, in their turn, have ever fresh problems to solve and new material to study. It becomes, then, of prime importance to every educated man, to ask what are the data of Ethics, what is the method by which its general principles are investigated, what are the considerations which the moralist ought to apply to the solution of the complex difficulties of life and action. And still, in spite of these obvious facts, ethical investigation, or any approach to an independent review of the current morality, is always unpopular with the great mass of mankind. Though the conduct of their own lives is the subject which most concerns men, it is that in which they are least patient of speculation. Nothing is so wounding to the self-complacency of a man of indolent habits of mind as to call in question any of the moral principles on which he habitually acts. Praise and blame are usually apportioned, even by educated men, according to vague and general rules, with little or no regard to the individual circumstances of the case. And of all innovators, the innovator on ethical theory is apt to be the most unpopular and to be the least able to secure impartial attention to his speculations. And hence it is that vague theories, couched in unintelligible or only half-intelligible language, and almost totally inapplicable to practice, have usually done duty for what is called a system of moral philosophy. The authors or exponents of such theories have the good fortune at once to avoid odium and to acquire a reputation for profundity.