The principle must not be a moral principle, because this would imply an organized opposition to morality on the other side, and the permanent existence of an immoral party; two parties always in active existence being plainly essential to the working of the system. You cannot, for example, have a party of purity, because this would imply, as its correlative and complement, a party of corruption, and it would be a grotesque arrangement to devote half your citizens permanently to the service and advocacy of corruption in order to maintain the machinery of your government.
The principle must be one of expediency. Parties, in other words, must be divided by some question of policy, about which honest men may differ. And it must be a question of sufficient magnitude to transcend in importance all other questions; of sufficient importance to warrant a man of sense and a good citizen in surrendering for its sake his private judgment on all other political subjects to the guidance of the party leader and the exigencies of the party struggle, and in doing his utmost to exclude from the legislature and the public service all men, however honest, however able, however useful in general respects to the country, who do not agree with him on the vital point. We need not use the invidious term proscription; the thing will be the same.
Now, it is manifest, in the first place, that the occurrence of such questions is exceptional, and not normal; they can seldom arise in fact except with reference to some organic change in the constitution, such as the transfer of supreme power from the crown to Parliament, or the change in the character of Parliament itself, embodied in the English Reform Bill of 1832. American slavery was an issue of a different kind and of still more transcendent importance; but it was one lying quite beyond the pale of ordinary politics. In normal times the occupations of legislatures and governments will be matters of current administration, not one of which is likely to form an issue of sufficient importance to swallow up all the rest and form a rational ground for the division of the nation into two organized parties struggling each to place its leaders in exclusive possession of the powers of the state.
In the second place, questions of expediency, however important, do not last forever; in one way or other they are settled and disappear from the political scene. Slavery dies and is buried. Parliamentary reform is carried out with all its corollaries, and becomes a thing of the past. What is to follow? Another question of sufficient importance to warrant a division of the nation into parties must be found. But suppose no such question exists, are we to manufacture one? That is the work to which the wire-pullers devote themselves in democracies governed by party, but the results seem hardly to correspond to our notion of the adamantine basis on which the political edifice is to rest forever.