Block on psychologism


  • [Required] Ned Block. 1981. Psychologism and Behaviorism. The Philosophical Review LXXXX, No. 1, January, 5-43. html
  • Frank Jackson. 1993. Block's Challenge. In David Malet Armstrong, John Bacon, Keith Campbell, Lloyd Reinhardt (eds.) Ontology, causality, and mind: essays in honor of D.M. Armstrong. Cambridge University Press.
  • Hanoch Ben-Yami (2005). Behaviorism and Psychologism: Why Block's Argument Against Behaviorism is Unsound. Philosophical Psychology 18 (2):179-186.


  • Having a mind is a matter of exhibiting the right kind of behavior.
  • Jackson

@the point of intelligence is to generate intelligent responses ... Being intelligent comes down to, when all is said and done, to facts about behaving intelligently.@

  • Standard objections: the stoic, the good actor


@Let psychologism be the doctrine that whether behavior is intelligent behavior depends on the character of the internal information processing that produces it. More specifically, I mean psychologism to involve the doctrine that two systems could have actual and potential behavior typical of familiar intelligent beings, that the two systems could be exactly alike in their actual and potential behavior, and in their behavioral dispositions and capacities and counterfactual behavioral properties (i.e., what behaviors, behavioral dispositions, and behavioral capacities they would have exhibited had their stimuli differed)--the two systems could be alike in all these ways, yet there could be a difference in the information processing that mediates their stimuli and responses that determines that one is not at all intelligent while the other is fully intelligent.@

  • Note the reference to potential behavior. Why is this relevant?


Blockhead is a machine that carries out conversations, but:

  • the conversations are all pre-programmed responses
  • it is basically a giant look-up tree
  • it is huge, but finite since there is only a finite number of possible conversations within a finite period of time
  • it might be technically / physically impossible to build, but the key assumption is that it is logically possible
  • Block says that it has "the intelligence of a toaster"



Frank Tipler on the physical impossibility of Blockhead (The Physics of Immortality):

@the human brain can code as much as 10^15 bits is correct, then since an average book codes about 10^6 bits, it would require more than 100 million books to code the human brain. It would take at least thirty five-story main university libraries to hold this many books. We know from experience that we can access any memory in our brain in about 100 seconds, so a hand simulation of a Turing Test-passing program would require a human being to be able to take off the shelf, glance through, and return to the shelf all of these 100 million books in 100 seconds. If each book weighs about a pound (0.5 kilograms), and on the average the book moves one yard (one meter) in the process of taking it off the shelf and returning it, then in 100 seconds the energy consumed in just moving the books is 3 x 1019 joules; the rate of energy consumption is 3 x 1011 megawatts. Since a human uses energy at a normal rate of 100 watts, the power required is the bodily power of 3 x 1015 human beings, about a million times the current population of the entire earth. A typical large nuclear power plant has a power output of 1,000 megawatts, so a hand simulation of the human program requires a power output equal to that of 300 million large nuclear power plants. As I said, a man can no more hand-simulate a Turing Test-passing program than he can jump to the Moon. In fact, it is far more difficult.@

  • But this is a description of an implementation of Blockhead using books. Does it really tell us that it is impossible to build a Blockhead?


Here is a possible reply to the Blockhead example:

(In Oppy, Graham, Dowe, David, "The Turing Test", The Stanford Encyclopedia of Philosophy (Fall 2008 Edition), Edward N. Zalta (ed.), URL = <>)

@The question of whether Blockhead is intelligent (has a mind, thinks) may seem straightforward, but—despite Block's confident assertion that Blockhead “has all of the intelligence of a toaster”—it is not completely obvious that we should deny that Blockhead is intelligent. True enough, Blockhead is a particularly inefficient processor of information; but it is at least a processor of information, and that—in combination with the behavior that is produced as a result of the processing of information—might well be taken to be sufficient grounds for the attribution of some level of intelligence to Blockhead.@

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