In practice these three kinds of arguments, which turn on moral, practical, and aesthetic considerations, tend to be much mingled.  The human mind is very complex, and our various interests and preferences are inseparably tangled.  The treacheries of self-analysis are proverbial, and are only less dangerous than trying to make out the motives of other people.  Accordingly we must expect to find that it is sometimes hard to distinguish between moral and aesthetic motives and practical, for the morality and the taste of a given people always in part grow out of the slow crystallizing of practical expediencies, and notions of morality change with the advance of civilization.

Furthermore, one must never forget that an argument of policy which does not involve and rest on subsidiary questions of fact is rare; and the questions of fact must be settled before we can go on with the argument of policy.  Before this country can intelligently make up its mind about the protective tariff, and whether a certain rate of duty should be imposed on a given article, a very complex body of facts dealing with the cost of production both here and abroad must be settled, and this can be done only by men highly trained in the principles of business and political economy.  Before one could vote intelligently on the introduction of a commission form of government into the town he lives in he must know the facts about the places in which it has already been tried.  It is not too much to say that there is no disputed question of policy into which there does not enter the necessity of looking up and settling pertinent facts.

On the other hand, there are some cases of questions of fact in which our practical interests deeply affect the view which we take of the facts.  In all the discussions of the last few years about federal supervision and control of the railroads it has been hard to get at the facts because of the conflicting statements about them by equally honest and well-informed men.  Where there is an honest difference of interest, as in every case of a bargain, the opposite sides cannot see the facts in the same way:  what is critically significant to the railroad manager seems of no great consequence to the shipper; and the railroad manager does not see the fixed laws of trade which make it impossible for the shipper to pay higher freight rates and add them to the price of his goods.  It is not in human nature to see the whole cogency of facts that make for the other side.  In all arguments, therefore, it must be remembered that we are; constantly swinging backward and forward from matters of fact to matters of policy.  In practice no hard-and-fast line separates the various classes and types; in the arguments of real life we mingle them naturally and unconsciously.