 Russell’s reply was unsatisfying to Bradley, who followed up with his “Reply to Mr Russell’s Explanations” in 1911, reiterating some of the same concerns. Namely, Bradley repeatedly returns to the worry about external relations—he finds them to be unobservable and unthinkable without the terms; a relation apart from its terms is indeed for Bradley an “indefensible abstraction”. In addition, he asks Russell to elaborate further on the presumed difference between an aggregate of entities and a unity of those entities. Bradley says that an appeal to relating relations is unsatisfying and further asks Russell to explain wherein the difference between relating relations and non-relating relations lies for him. But for Russell there was no further story to be told; the difference between relating and non-relating relations is a primitive on which he did not feel the need to offer any further details. 