The lack of a proper identity concept for attributes is a lack that phi losophers feel impelled to supply; for, what sense is there in saying that there are attributes when there is no sense in saying when there is one at tribute and when two Carnap and others have proposed this principle for identifying attri butes: two sentences about attribute the same attri bute to if and only if the two sentences arc not merely alike in truth value for each choice of, but necessarily and a nalytically so, by sameness of meaning.'