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Selected Books by Edmund Blair Bolles

  • Galileo's Commandment: 2500 Years of Great Science Writing
  • The Ice Finders: How a Poet, a Professor, and a Politician Discovered the Ice Age
  • Einstein Defiant: Genius vs Genius in the Quantum Revolution

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Aren't you just perpetuating this story about starlings understanding recursive CFGs with this article? Chomsky stated the facts clearly. They discovered, yet again, that animals can 'count' (subitize). It might be interesting to see how long a bird can keep a number in its head, but not to people examining language. Just because you can understand one rule which can be implemented in a CFG doesn't mean you understand as a CFG.

BTW, great blog... I'm loving the way that this is starting.




Thanks for the good words. You’re plainly an informed commenter. What do you think? Was the experiment in Hauser-Chomsky-Fitch unambiguous in its demonstration of recursive thinking among humans or might there have been some other explanation there too?

By the way, for visitors who are not as well informed on the jargon, CFG refers to context-free grammar. That’s a formal grammar that allows for the production of recursive sentences.


I haven't read the Gentner et al. article, but an experiment that needs to use 12,000 trials to get an animal to do something seems somewhat dodgy to me - without knowing their procedures, the animals may well be picking up some other cue to recursion/non-recursion. Regardless, Chomsky's position would be that we are predisposed to detecting recursion (especially considering all that stuff about FOXP2, and in the article they point to the statistical learning paradigm of Jenny Saffran as a learning mechanism for recursion). That it takes 12,000 trials for a starling to distinguish recursion indicates that the starling is probably not predisposed in the same way that we are.

With that in mind, I do have problems with HCF's position. Firstly, they argued that recursion is not only unique to humans but unique to language, that only language uses that module. This something which is clearly negated by the presence of music and dance in humans, which are also recursive but not language. Something else that comes out quite clearly when you consider Pinker and Jackendoff's reply to the paper (and HCF's reply to that) is that HCF believe that recursion's uniqueness to humans is very good evidence of language being evolved. It could, however, simply be that it's not the presence of recursion as such that makes language language, nor the presence of certain grammatical formations (and so on, see P&J's reply for a more detailed list) - but instead the combination of all of these things. Seems like no other animal is capable of all of the other components of language in quite the same way we are, though I'm sure that some animal somewhere is capable and predisposed to each individual aspect of language in some way.



Actually, HCF do not argue that recursion is unique to the language faculty. Quite the opposite. They are very clear about stating that they think recursion is behind the ability to count natural numbers to infinity and weakly suggest it underlies music composition and comprehension as well.

As for the experiments on starlings and tamarins, the experiments of Hauser do not prove once and for all that nonhuman primates don't have recursion, but then again they don't have to. In light of the claim that only humans have recursion, the onus is on experimenters to show that any other animal has it as well. As noted, the starling experiment doesn't hold up.

The definition of recursion as understood in CHF is that a recursive systems yields an output of discrete infinity. The fact that we can construct (in principle) infinitely long sentences and infinitely embedded structures, as well as the fact that we can count to infinity, is proof we have recursion.

One development that has occured since the article was published, is that the claim that nonhuman primates do not have an instinctive ability to immitate has been disproven, at least with regard to facial movements (though not yet with regard to vocalizations). You can find that article here.


“The fact that we can construct (in principle) infinitely long sentences and infinitely embedded structures, as well as the fact that we can count to infinity, is proof we have recursion.”

There is the numb of the argument and I have to confess I have never been persuaded of the truth of this orthodox position, at least as far as it stands about syntax. No editor would accept a sentence like, “I don’t believe that you don’t believe that he doesn’t believe that a middle-aged man who bit a mangy dog covered in strange fleas contracted from a visit to a passing three-ring circus where imported, Asian elephants bellowed at the unhappily married and sadly childless Mahout, also bumped his nose.” The limit to understanding this sentence is precisely, memory. We get lost and forget what was being discussed.

This is a good example of the syntax vs semantics conflict. If you think syntax is all, then the notion of an infinite sentence isn’t troubling. If meaning and understanding are part of your idea of language, the idea becomes nonsensical.


As you say, the problem with your sentence is memory, but arguably that is unrelated to linguistic ability. To deny that possibility seems to put an unecessary limit on research goals, and I can't think of a good reason to suppose that our on-line memory capacity should say anything about our ability to produce infinitely long sentences.

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