Further notes about CardWorld

Why CardWorld is not a "toy" example

CardWorld is an example from a sub-field of computational linguistics which can be called experimental linguistics or language simulation.  It differs from the related fields of theoretical linguistics, psycholinguistics, and language engineering in that its objective is to implement detailed working models of cognitive mechanisms by which humans understand and use natural languages.

• Its pragmatic domain, though simple, feels quite "natural" to a human user and can be extended in various directions.  It is a minimal but reasonably self-contained pragmatic domain.  Playing cards are all the same size, and although cards are almost two-dimensional, they can cover one another, making for interesting non-permanent collections.  Most people already know about cards and how to manipulate them.  They know that cards are two-sided flat objects that can be moved around, turned over, shuffled, and stacked.  The first implemented version of CardWorld, CardWorld1 (like its refined implementation CardWorld1a), does not even require knowledge about playing cards, because it only deals with cards as simulated physical objects.  The next implemented version, CardWorld2, does require knowledge of standard features of playing cards (suits, ranks, colors, face cards, spot cards, and jokers) as they are used in English-speaking countries.
  
• Because the pragmatic domain is reasonably simple, it can be modeled thoroughly, with few additional simplifying assumptions.  That permits the focus of the CardWorld project to be on modeling the syntax, semantics, and pragmatics of English-language interactions with it or, more accurately, with a simulated card agent playing the role of a person.  Yet the pragmatic domain is rich enough to support many aspects of English syntax and semantics, including many extensions beyond the aspects modeled in CardWorld1 and CardWorld2.  

What CardWorld1 and CardWorld2 illustrate about and provide working models of aspects of natural-language understanding

• Understanding a natural language is not an all-or-nothing ability.  In the beginning it does not require recursively nested syntax, the ability to perform deductive logic, and other abilities that are required for the full fluency of a well-educated adult.  We know that, of course, from the language abilities of children.  In most cases the CardAgent component of CardWorld1 understands the utterances that it accepts as well as, and in the same way as, a person would.  To the extent that its understanding differs from that of most persons, it simply needs correction and refinement.
  
• The only requirements for communication by means of a language are: (1) a shared pragmatic environment, (2) an ability to exchange utterance tokens, (3) vocabulary, parsing and interpretation abilities which have enough in common between the interlocutors that the intended pragmatic effects of utterance actions can be accomplished.  CardWorld1 meets all those requirements.
  
• CardWorld1 models some specific subtleties about direct-definite, deictic and anaphoric reference in English:

1. The type of thing referred to, as well as the instance referred to, can be anaphoric.  e.g. "Turn over this pile."  "Now turn over that one."  ("one" refers to "pile")
   
2. Singular separate reference can be anaphoric.  e.g. "Turn over each pile."  "Then shuffle it and spread it out."  ("it" refers to each pile separately.)
3. Definite reference with the unique quantifier "the" can refer to the only instance, among a set of instances, to which the action specified by the verb can be applied.  e.g. "shuffle the pile" when there is one multi-card pile and one or more separate singleton cards.  (A pile consisting of a single card can't be shuffled.)
   
4. Definite reference with the unique quantifier "the" can refer to the unique non-degenerate instance among a set of instances, all but one of which are degenerate.  e.g. "turn over the pile" when there is a multi-card pile as well as some singleton cards.  (This differs from example 3, because singleton cards can be turned over.)
   
5. Definite reference with the unique quantifier "the" can refer to an instance which is separate from one or more collections of two or more instances of the same type.  e.g. "turn over the card" when there is one card alone by itself while the other cards are in multi-card piles.
6. Reference with the unique quantifier "the" can be deictic if it would otherwise be ambiguous except that there is an instance of the type which has recently been singled out.  e.g. move a card, then "turn over the card".

• CardWorld2 models some additional subtleties in reference that involve shifts of attention from parts (cards) to wholes (piles) and from wholes (piles) to parts (cards) with described properties.  Its software agent, CardAgent2, also models an omniscient Card God (or, if you prefer, a Card Superhero), which knows where all of the cards are on the table regardless of whether they are face up, face down, or stacked in piles, and which can manipulate them regardless of where they are within piles.  Later versions of CardWorld will attempt to model also more-limited software agents, which will be called Card Players, with more human-like abilities.