One dumb-bell, Watson! Consider an athlete with one dumb-bell. Picture to yourself the unilateral development - the imminent danger of a spinal curvature. Shocking, Watson, shocking!
The ideal reasoner, he remarked, would, when he had once been shown a single fact in all its bearings, deduce from it not only all the chain of events which led up to it but also all the results which would follow from it.