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 hold from those which hold in this one, then plainly a precisely similar action done in precisely similar circumstances might yet have different total effects. According to our principle, therefore, the statement that any two precisely similar actions, done in precisely similar circumstances, must both be right, if one is right, though true as applied to this Universe, provided (as is commonly supposed) the laws of nature cannot change, is not true absolutely unconditionally. But our principle asserts absolutely unconditionally that if it is once right to prefer a set of total effects A to another set B, it must always, in any conceivable Universe, be right to prefer a set precisely similar to A to a set precisely similar to B.

This, then, is a second very fundamental principle, which our theory asserts—a principle which is, in a sense, concerned with classes of actions, and not merely with particular actions. And in asserting this principle also it seems to me that our theory is right. But many different views have been held, which, while admitting that one and the same action cannot be both right