Please note that the content of this book primarily consists of articles available from Wikipedia or other free sources online. In psychology, temperament refers to those aspects of an individual''s personality, such as introversion or extroversion, that are often regarded as innate rather than learned. A great many classificatory schemes for temperament have been developed; none, though, has achieved general consensus in academia. Historically, the concept of temperament was part of the theory of the four humours, with their corresponding four temperaments. The concept played an important part in pre-modern psychology, and was explored by philosophers such as Immanuel Kant and Hermann Lotze. David W. Keirsey also drew upon the early models of temperament when developing the Keirsey Temperament Sorter. More recently, scientists seeking evidence of a biological basis of personality have further examined the relationship between temperament and character (defined in this context asthe learnt aspects of personality). However, biological correlations have proven hard to confirm.