text: **Defining artificial intelligence**
  Alan Turing wrote in 1950 "I propose to consider the question 'can machines think'?"[359] He advised 
  changing the question from whether a machine "thinks", to "whether or not it is possible for machinery to 
  show intelligent behaviour".[359] He devised the Turing test, which measures the ability of a machine to 
  simulate human conversation.[323] Since we can only observe the behavior of the machine, it does not 
  matter if it is "actually" thinking or literally has a "mind". Turing notes that we can not determine these 
  things about other people but "it is usual to have a polite convention that everyone thinks."[360] 
  
  Russell and Norvig agree with Turing that intelligence must be 
  defined in terms of external behavior, not internal structure.[1] 
  However, they are critical that the test requires the machine to 
  imitate humans. "Aeronautical engineering texts", they wrote, "do 
  not define the goal of their field as making 'machines that fly so 
  exactly like pigeons that they can fool other pigeons.' "[362] AI 
  founder 
  that "Artificial 
  intelligence 
  is not, by definition, simulation of human 
  intelligence".[363] 
  
  John McCarthy agreed, writing 