Re: 3vl 2vl and NULL

On 4 Dec 2005 16:36:54 -0800, JOG wrote:

>
>Roy Hann wrote:
>[snip]
>> If you have a Boolean variable then you know that its missing value must be
>> drawn from only the Boolean domain. The appropriate way to think of the
>> missing information is therefore not as an empty set, but as something that
>> is simultaneously all possible values from the Boolean domain. The Boolean
>> variable thus might be T, F, or T/F (where T/F is a kind of superposition of
>> all permissible Boolean values).
>[/snip]
>
>I wonder if you are heading for a more probabilistic approach here? I'd
>contest that something can simultaneously possess all possible boolean
>values, but it can certainly have an equal probability of being one of
>those values (Schroedinger's boolean?). That would allow a
>probabilistic truth table:
>
>T & T = 100% T
>T & F = 100% F
>F & F = 100% F
>T & U = 75%T 25% F
>F & U = 25%T 75% F
>U & U = 50%T 50% F
>
>I suggest this only out of curiosity (to my mind a missing field means
>no matching proposition full stop, but lets leave all that m'larkey to
>the other thread).

Hi JOG,

I'm sorry, but the probabilistic truth table makes no sense at all.

Let's start with this:

>T & U = 75%T 25% F

Okay. You don't know my age. You do know that 5 > 4. Now consider the proposition

  (5 > 4) & (Hugo OLDER THAN 40)

With your probabilistic truth table, this whole expression has a 75% chance to be true - so there's abviously a 75% chance that I'm older than 40. Based on what? And how would my chance to be over 40 change if I use this expresion:

 (5 > 4) & (6 < 7) & (2 = 2) & (3 != 5) & (Hugo OLDER THAN 40)

But it gets worse. Let's move to

>F & U = 25%T 75% F

And consider

  (5 = 4) & (Hugo OLDER THAN 40)

According to the probabilistic truth table, there's a 25% chance that this expression is true. Well, I can tell you - if I ever reach the age where 5 suddenly becomes equal to 4, I'll seak suicide.

Best, Hugo

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