XVII. It is necessary to observe that a war may be just in its origin, and yet the intentions of its authors may become unjust in the course of its prosecution. For some other motive, not unlawful IN ITSELF, may actuate them more powerfully than the original right, for the attainment of which the war was begun. It is laudable, for instance, to maintain national honour; it is laudable to pursue a public or a private interest, and yet those objects may not form the justifiable grounds of the war in question. A war may gradually change its nature and its object from the prosecution of a right to the desire of seconding or supporting the aggrandizement of some other power. But such motives, though blamable, when even connected with a just war, do not render the war ITSELF unjust, nor invalidate its conquests. CHAPTER XXIII. ON DOUBTFUL CAUSES. Origin of moral doubts--The dictates of conscience, though erroneous, not to be violated--Opposite opinions supported by argument, or by authority--In doubtful and important matters the safer side of the question to be followed--In such cases it is right to abstain from war--Disputes settled by conference or arbitration--Christian duties--Whether single combat is allowable in order to avoid war--In cases of equal doubt the claims of the present possessor to be preferred--Where neither party is in possession, claims to be divided--Whether a war can be just on both sides, explained by a distinction. I. There is much truth in Aristotle's observation that moral reasonings can never amount to the certainty of mathematical demonstration. Because in mathematical reasoning, all the figures are considered in the abstract, purely by themselves, and without relation to the circumstances of time or place, so that there is nothing to warp the judgment from the object immediately under consideration. Besides the figures in general form a direct contrast to each other. Thus, for instance, there is no intermediate line between a straight line and a curve. But it is not so in morals, where the least circumstances vary the subject, and admit a latitude of interpretation, settling the points of truth and justice between two extremes. So that between what is right and what is unlawful there is a middle space, where it is easy to incline to the one side, or to the other. This occasions an ambiguity somewhat like the difficulty of deciding the precise moment, where the twilight begins, and where it ends. From hence Aristotle concludes that it is sometimes difficult to determine, between two extremes, what line of conduct ought to be chosen or rejected.