A definite order obtains among mental phenomena, just as among material
phenomena; and there is no more chance, nor any accident, nor uncaused
event, in the one series than there is in the other. Moreover, there is
a connection of cause and effect between certain material phenomena and
certain mental phenomena. Thus, for example, certain sensations are
always produced by the influence of particular material bodies on our
organs of sense. The prick of a pin gives pain, feathers feel soft,
chalk looks white, and so on. The study of mental phenomena, of the
order in which they succeed one another, and of the relations of cause
and effect which obtain between them and material phenomena, is the
province of the science of =Psychology=.
All the phenomena of nature are either material or immaterial, physical
or mental; and there is no science, except such as consists in the
knowledge of one or other of these groups of natural objects, and of the
relations which obtain between them.