For we conceive it as the aim of a philosopher, as such, to do somewhat more than define and formulate the common normal opinions of mankind. His function is to tell men what they ought to think, rather than what they do think: he is expected to transcend Common Sense in his premises, and is allowed a certain divergence from Common Sense in his conclusions. It is true that the limits of this deviation are firmly, though indefinitely, fixed: the truth of a philosopher's premises will always be tested by the acceptability of his conclusions: if in any important point he be found in flagrant conflict with common opinion, his method is likely to be declared invalid. Still, though he is expected to establish and concatenate at least the main part of the commonly accepted moral rules, he is not necessarily bound to take them as the basis on which his own system is constructed. Rather, we should expect that the history of Moral Philosophy--so far at least as those whom we may call orthodox thinkers are concerned--would be a history of attempts to enunciate, in full breadth and clearness, those primary intuitions of Reason, by the scientific application of which the common moral thought of mankind may be at once systematized and corrected.