Whatever exists at all exists in some amount. To know it thoroughly involves knowing its quantity as well as its quality.

For origin and development of human faculty we must look to these processes of association in lower animals.

When, instead of merely associating some act with some situation in the animal way, we think the situation out, we have a set of particular feelings of its elements.

Psychology helps to measure the probability that an aim is attainable.

To the intelligent man with an interest in human nature it must often appear strange that so much of the energy of the scientific world has been spent on the study of the body and so little on the study of the mind.

The restriction of studies of human intellect and character to studies of conscious states was not without influence on a scientific studies of animal psychology.

It will of course, be understood that directly or indirectly, soon or late, every advance in the sciences of human nature will contribute to our success in controlling human nature and changing it to the advantage of the common wheel.