 Broad holds, then, that neither ‘could have acted differently’ nor ‘could have willed differently’ can be given a conditional analysis. Having discarded conditional types of substitutability he turns to categorical substitutability. If an action is obligable it must be substitutable in a categorical sense. “We must be able to say of an action, which was done, that it could have been avoided, in some sense of ‘could’ which is not definable in terms of ‘would have, if’” (1934, p. 204). Note that the quoted passage merely states that categorical substitutability is a necessary condition of obligability. It is clear, however, that Broad also takes it to be a sufficient condition. Thus, his position is that,