The domain of psychology comprises the phenomena that we may call conscious or psychological reactions. By psychological reactions we mean the responses which psychological organisms, such as human individuals and higher types of animals, perform when they adjust themselves to the various stimulating objects surrounding them. A few of the topics in this book include: the primary data of psychology; the nature of basic conduct and how it is developed; the nature of sensing and perceiving; the nature of volitional conduct; the psychology of language; and the behaviour of the organism during sleep.