Chapter 4

in speaking of the mind we cannot always distinguish differences of kind from differences of degree; nor have we any measure of the strength and intensity of our ideas or feelings.

j. Although heredity has been always known to the ancients as well as ourselves to exercise a considerable influence on human character, yet we are unable to calculate what proportion this birth-influence bears to nurture and education. But this is the real question. We cannot pursue the mind into embryology: we can only trace how, after birth, it begins to grow. But how much is due to the soil, how much to the original latent seed, it is impossible to distinguish. And because we are certain that heredity exercises a considerable, but undefined influence, we must not increase the wonder by exaggerating it.

k. The love of system is always tending to prevail over the historical investigation of the mind, which is our chief means of knowing it. It equally tends to hinder the other great source of our knowledge of the mind, the observation of its workings and processes which we can make for ourselves.