One further addition is required for the definition of the objectively right act, namely, that it must be possible. Among the acts whose consequences are to be considered we must not include such as are either physically impossible to perform or impossible for the agent to think of. This last condition introduces difficulties connected with determinism, which are discussed in Section IV. Ignoring these difficulties, we may say that the objectively right act is that one which, of all that are possible, will probably have the best consequences. (§ 18 ¶ 1)