• “The capacity for knowledge, and knowledge possessed.” V. A. C. Henmon [Henmon:21]
• “… cognitive ability.” R. J. Herrnstein and C. Murray [Herrnstein:96]
• “… the resultant of the process of acquiring, storing in memory, retrieving, combining, comparing, and using in new contexts information and conceptual skills.” Humphreys
• “Intelligence is the ability to learn, exercise judgment, and be imaginative.” J. Huarte
• “Intelligence is a general factor that runs through all types of performance.” A. Jensen
• “Intelligence is assimilation to the extent that it incorporates all the given data of experience within its framework … There can be no doubt either, that mental life is also accommodation to the environment. Assimilation can never be pure because by incorporating new elements into its earlier schemata the intelligence constantly modifies the latter in order to adjust them to new elements.” J. Piaget [Piaget:63]
• “Ability to adapt oneself adequately to relatively new situations in life.” R. Pinter quoted in [Sternberg:00]
• “A biological mechanism by which the effects of a complexity of stimuli are brought together and given a somewhat unified effect in behavior.” J. Peterson quoted in [Sternberg:00]
• “… certain set of cognitive capacities that enable an individual to adapt and thrive in any given environment they find themselves in, and those cognitive capacities include things like memory and retrieval, and problem solving and so forth. There’s a cluster of cognitive abilities that lead to successful adaptation to a wide range of environments.” D. K. Simonton [Simonton:03]
• “Intelligence is part of the internal environment that shows through at the interface between person and external environment as a function of cognitive task demands.” R. E. Snow quoted in [Slatter:01]
• “… I prefer to refer to it as ‘successful intelligence.’ And the reason is that the emphasis is on the use of your intelligence to achieve success in your life. So I define it as your skill in achieving whatever it is you want to attain in your life within your sociocultural context --- meaning that people have different goals for themselves, and for some it’s to get very good grades in school and to do well on tests, and for others it might be to become a very good basketball player or actress or musician.” R. J. Sternberg [Sternberg:03]
• “… the ability to undertake activities that are characterized by (1) difficulty, (2) complexity, (3) abstractness, (4) economy, (5) adaptedness to goal, (6) social value, and (7) the emergence of originals, and to maintain such activities under conditions that demand a concentration of energy and a resistance to emotional forces.” Stoddard
• “The ability to carry on abstract thinking.” L. M. Terman quoted in [Sternberg:00]
• “Intelligence, considered as a mental trait, is the capacity to make impulses focal at their early, unfinished stage of formation. Intelligence is therefore the capacity for abstraction, which is an inhibitory process.” L. L. Thurstone [Thurstone:24]
• “The capacity to inhibit an instinctive adjustment, the capacity to redefine the inhibited instinctive adjustment in the light of imaginally experienced trial and error, and the capacity to realise the modified instinctive adjustment in overt behavior to the advantage of the individual as a social animal.” L. L. Thurstone quoted in [Sternberg:00]
• “A global concept that involves an individual’s ability to act purposefully, think rationally, and deal effectively with the environment.” D. Wechsler [Wechsler:58]
• “The capacity to acquire capacity.” H. Woodrow quoted in [Sternberg:00]
• “… the term intelligence designates a complexly interrelated assemblage of functions, no one of which is completely or accurately known in man …” R. M. Yerkes and A. W. Yerkes [Yerkes:29]
• “… that faculty of mind by which order is perceived in a situation previously considered disordered.” R. W. Young quoted in [Kurzweil:00]
AI researcher definitions
This section lists definitions from researchers in artificial intelligence.
• “… the ability of a system to act appropriately in an uncertain environment, where appropriate action is that which increases the probability of success, and success is the achievement of behavioral subgoals that support the system’s ultimate goal.” J. S. Albus [Albus:91]
• “Any system … that generates adaptive behviour to meet goals in a range of environments can be said to be intelligent.” D. Fogel [Fogel:95]
• “Achieving complex goals in complex environments” B. Goertzel [Goertzel:06]
• “Intelligent systems are expected to work, and work well, in many different environments. Their property of intelligence allows them to maximize the probability of success even if full knowledge of the situation is not available. Functioning of intelligent systems cannot be considered separately from the environment and the concrete situation including the goal.” R. R. Gudwin [Gudwin:00]
• “[Performance intelligence is] the successful (i.e., goal-achieving) performance of the system in a complicated environment.” J. A. Horst [Horst:02]
• “Intelligence is the ability to use optimally limited resources -- including time -- to achieve goals.” R. Kurzweil [Kurzweil:00]
• “Intelligence is the power to rapidly find an adequate solution in what appears a priori (to observers) to be an immense search space.” D. Lenat and E. Feigenbaum [Lenat:91]
• “Intelligence measures an agent’s ability to achieve goals in a wide range of environments.” S. Legg and M. Hutter [Legg:06ior]
• “… doing well at a broad range of tasks is an empirical definition of ‘intelligence’ ” H. Masum [Masum:02]
• “Intelligence is the computational part of the ability to achieve goals in the world. Varying kinds and degrees of intelligence occur in people, many animals and some machines.” J. McCarthy [McCarthy:04]
• “… the ability to solve hard problems.” M. Minsky [Minsky:85]
• “Intelligence is the ability to process information properly in a complex environment. The criteria of properness are not predefined and hence not available beforehand. They are acquired as a result of the information processing.” H. Nakashima [Nakashima:99]
• “… in any real situation behavior appropriate to the ends of the system and adaptive to the demands of the environment can occur, within some limits of speed and complexity.” A. Newell and H. A. Simon [Newell:76]
• “[An intelligent agent does what] is appropriate for its circumstances and its goal, it is flexible to changing environments and changing goals, it learns from experience, and it makes appropriate choices given perceptual limitations and finite computation.” D. Poole [Poole:98]
• “Intelligence means getting better over time.” Schank [Schank:91]
• “Intelligence is the ability for an information processing system to adapt to its environment with insufficient knowledge and resources.” P. Wang [Wang:95]
• “… the mental ability to sustain successful life.” K. Warwick quoted in [Asohan:03]
• “… the essential, domain-independent skills necessary for acquiring a wide range of domain-specific knowledge -- the ability to learn anything. Achieving this with ‘artificial general intelligence’ (AGI) requires a highly adaptive, general-purpose system that can autonomously acquire an extremely wide range of specific knowledge and skills and can improve its own cognitive ability through self-directed learning.” P. Voss [Voss:05]
Is a single definition possible?
In matters of definition, it is difficult to argue that there is an objective sense in which one definition could be considered to be the correct one. Nevertheless, some definitions are clearly more concise, precise and general than others. Furthermore, it is clear that many of the definitions listed above are strongly related to each other and share many common features. If we scan through the definitions pulling out commonly occurring features we find that intelligence:
• Is a property that an individual agent has as it interacts with its environment or environments.
• Is related to the agent’s ability to succeed or profit with respect to some goal or objective.
• Depends on how able the agent is to adapt to different objectives and environments.
Putting these key attributes together produces the informal definition of intelligence that we have adopted,
“Intelligence measures an agent’s ability to achieve goals in a wide range of environments.” S. Legg and M. Hutter
Features such as the ability to learn and adapt, or to understand, are implicit in the above definition as these capacities enable an agent to succeed in a wide range of environments. For a more comprehensive explanation, along with a mathematical formalisation of the above definition, see [Legg:06ior] or our forthcoming journal paper.
References
• Albus:91 J. S. Albus. Outline for a theory of intelligence. IEEE Trans. Systems, Man and Cybernetics, 21(3):473--509, 1991.