(from the chapter) The term aptitude, according to most dictionaries, is derived from the Latin term aptitudo, meaning fitness. The psychological use of the term is similar in that it has traditionally referred to a potential for acquiring knowledge or skill. Traditionally, aptitudes are described as sets of characteristics that relate to an individual’s ability to acquire knowledge or skills in the context of some training or educational program. There are two important aspects of aptitude to keep in mind. First, aptitudes are present conditions (i.e., existing at the time they are measured). Second, there is nothing inherent in the concept of aptitudes that says whether they are inherited or acquired or represent some combination of heredity and environmental influences. Also, aptitude tests do not directly assess an individual’s future success; they are meant to assess aspects of the individual that are indicators of future success. That is, these measures are used to provide a probability estimate of an individual’s success in a particular training or educational program. While the meaning of aptitude is well delineated, there is much controversy over how to distinguish aptitude tests from other kinds of psychometric measures, specifically intelligence and achievement tests, partly because the major salient difference between intelligence, aptitude, and achievement tests has to do with the purpose of testing rather than with the content of the tests. What makes an assessment instrument an aptitude test rather than an intelligence or achievement test is mainly the future orientation of the predictions to be made from the test scores.