LINGUIST List 12.1345

Thu May 17 2001

Disc: New: How do you demonstrate recursion?

Editor for this issue: Karen Milligan <>


  1. Dorothea Cogill, How do you demonstrate recursion?

Message 1: How do you demonstrate recursion?

Date: Wed, 16 May 2001 13:19:51 +1100
From: Dorothea Cogill <>
Subject: How do you demonstrate recursion?

What does it take for someone or something to show a grasp of recursive rules?

Assume you have a communication system in which some symbols stand for
actions (let's make those symbols the vowels A E I O & U, but they could be
anything you please), and other symbols stand for objects to which the
actions can be applied (let's make these symbols the consonants of the
alphabet - whatever). Put two symbols in order, and they amount to a
command to perform that action on that object. The correct order is set;
say it's ACTION + OBJECT, for example. Then (for the symbols offered
above) a string like "A Q" is a command to perform action A on object Q;
throw a ball, for example, if A is 'throw' and Q is 'ball'.

Now, you give these commands to your subject - perhaps a very young child,
or a computer, or a smart dog - and they perform them correctly. Then, for
the first time, you give two commands at once; you might say "AQEP" , for
example. Your subject then goes off and performs action A on object Q and
follows this by performing action E on object P.

The question is - well, I guess there are two questions.
1. does your system possess recursion? After all, if a sentence S is
ACTION + OBJECT, then two in a row can be written S-> S(S), which can be
expanded indefinitely (I hope your computer is translating these symbols
2. does your subject show a grasp of recursive rules in responding to the
command correctly?

No other examples of recursion have been created or tested for this system
and this subject; this is the only one you have to go on.

What do you think?
Mail to author|Respond to list|Read more issues|LINGUIST home page|Top of issue