The two certainties differ not in degree only but in kind; and mathematical demonstration having to do only with thoughts, the creation of pure mind, cannot in the slightest degree be affected by any complete or incomplete realization of these thoughts in any time, past, present, or to come. When I say that all the angles of a triangle are equal to two right angles, or that the angle at the centre of a circle is double the angle at the circumference, I prove this from certain necessary relations of lines to lines drawn under conditions of which my thought is the absolute master. The proof is only the evolution of what lies in the thing,--of what cannot be otherwise, so long as the figure remains subject to the dictatorial power of my conception. It will be now quite evident from these specimens, that Hartley’s philosophy is just the sensuous side of Locke worked curiously into detail, with a practical rejection of the intellectual side. Indeed, he says expressly (i. 360) that “all our most complex ideas arise from sensation, and REFLECTION IS NOT A DISTINCT SOURCE, as Mr. Locke makes it.” This throwing of reflection overboard is the necessary postulate of all the absurdity that afterwards grew out from the Lockian philosophy; and James Mill accordingly[289.1] disowns the “ideas of reflection” with {290} the same fatal one-sideness, and, it may be added, with the same transparent superficiality of logic; for when a man talks of “generalizing states of consciousness,” what is this but another term for reflection? Generalizing is a species, and one of the most universally practised species, of reflection.