18 Part I Introduction
∙ Six criteria determine the usefulness of a scientific theory: (1) Does the
theory generate research? (2) Is it falsifiable? (3) Does it organize and
explain knowledge? (4) Does it suggest practical solutions to everyday
problems? (5) Is it internally consistent? and (6) Is it simple or
parsimonious?
∙ Each personality theorist has had either an implicit or explicit concept of
humanity.
∙ Concepts of human nature can be discussed from six perspectives:
(1) determinism versus free choice, (2) pessimism versus optimism,
(3) causality versus teleology, (4) conscious versus unconscious
determinants, (5) biological versus social factors, and (6) uniqueness
versus similarities in people.