Normal, irrational, likely, legal plays

The forums (RGB, IBLF, BLML, BBO) are awash with discussions of claims, as ever. I can not resist a posting on the different classes of plays that the (current) claim laws require a TD to consider.

1997 Laws

In the 1997 laws there is

• "normal" (Laws 69, 70 and 71), includes careless or inferior but not irrational (footnote 20);
• "irrational" (end of Law 70E), because of the footnote I had interpreted this as the opposite of normal (probably erroneously);
• "legal" (Law 71A), I think we understood this and, with the proper interpretation of Law 71, we did not need to distinguish this from "normal".

So, with my naive understanding of "irrational" in Law 70E, we only needed to understand what was or was not "normal", as in "normal play of the remaining cards" or "normal line of play".

2007 Laws

Now, in the 2007 laws there are again three different classes of plays, but now I think they are all independent.

• "likely" (Law 69B), a clear change from 1997;
• "normal" (Laws 70 and 71), includes careless or inferior (footnote 22);
• "irrational" (Law 70E1), without this word occurring in the footnote.

The change from "normal" to "likely" in Law 69, and the removal of "irrational" from footnote 22, indicates to me that there are now three independent tests to be applied in Laws 69, 70, and 71. For now all I can do is record the different terms, we will have to await experience, case law, and interpretation to distiguish them.

Bounded rationality

It is clear in that "irrational" in the 1997 laws could not interpreted literally, leading the Ace from A10xx opposite KQ9xx was normal but also irrational. A friend, bridge partner, and mathematician who mixes with economists, introduced me to the concept of bounded rationality which is used by economists and game theorists to label some kinds of irrational behaviour from supposedly rational agents. The idea is that rational agents (e.g. humans) don't have time/effort/inclination to calculate the correct rational response in a given situation, so there is a bound on the agents' rationality which does not allow the agent to complete the calculation, and may lead them to behave irrationally.

In understanding how we describe claims ruling, it is useful to think that some normal plays (including careless or inferior) could be classed as boundedly rational while remaining strictly irrational. I don't know whether this concept would help in interpreting "irrational" in Law 70E1.