What is the difference between two schools of design?

On the appeal much was made of the proposition that there were two schools of design, one that did not include internal reinforcement and permitted internal cracking of towers and one that included internal reinforcement and permitted external cracking. The reason for this argument, of course, is that if there is a substantial body of professional opinion supporting a method of operation, a professional cannot be charged with a negligent breach of his duty of care by reason only that he employed that method: see Wilson v. Swanson (1956), 1956 CanLII 1 (SCC), 5 D.L.R. (2d) 113 at pp. 119-20, [1956] S.C.R. 804 at p. 812, per Rand J. Even assuming there were two schools, there was, as we saw, ample evidence to justify the trial judge's finding of negligence.