"The ability to carry out abstract thinking." (Terman, 1921)
 

"The capacity for knowledge, and knowledge possessed."(Henmon, 1921)
 

"Intelligence is a general factor that runs through all types of performance." (unknown)
 

"A global concept that involves an individual's ability to act purposefully, think rationally, and deal effectively with the environment." (Wechsler, 1958).
 

 "The capacity to learn or to profit by experience."(Dearborn, 1921)
 

"Intelligence is adaptation to the environment."(unknown)
 

"A person possesses intelligence insofar as he had learned, or can learn, to adjust himself to his environment."
(Colvin, cited in Sternberg, 1982, p.30)
 

"Intelligence is the ability to use optimally limited resources - including time - to achieve goals." (Kurzweil, 1999)
 

"Intelligent activity consists of grasping the essentials in a given situation and responding appropriately to them." (unknown)
 

 "Intelligence is a hypothetical idea which we have defined as being reflected by certain types of behaviour." (unknown)
 

"The capacity to acquire capacity." (Woodrow, 1921)
 

"Intelligence is what is measured by intelligence tests." (Boring, 1923)
 

"Intelligence is that faculty of mind by which order is perceived in a situation previously considered disordered."
(R.W. Young, cited in Kurzweil, 1999)
 

"Intelligence is what you do when you don't know what to do." (unknown)