Psychology is generally considered to be the science of mind, although

more properly it is the science of mental states—thoughts,

feelings, and acts of volition. It was formerly the custom of writers

on the subject of psychology to begin by an attempt to define and

describe the nature of mind, before proceeding to a consideration

of the subject of the various mental spates and activities. But more

recent authorities have rebelled against this demand, and have

claimed that it is no more reasonable to hold that psychology

should be held to an explanation of the ultimate nature of mind

than it is that physical science be held to an explanation of the ultimate

nature of matter.