Message-Id: <m0r8sHf-00005XC@xiron.pc.helsinki.fi>
Date:         Sat, 19 Nov 1994 11:04:16 EST
Reply-To:     bob@GNU.AI.MIT.EDU
Sender:       Lojban list <LOJBAN%CUVMB.bitnet@FINHUTC.hut.fi>
From:         bob@GNU.AI.MIT.EDU
Subject:      Re: da'i
To:           Veijo Vilva <veion@XIRON.PC.HELSINKI.FI>
Content-Length: 1597
Lines: 36

pc said:

    ... I am stopped by questions like,
    if a sentence means different things depending on whether
    it is true or false, how do we find out whether it is true or false,
    since we have to know what it means to make that determination? ..

Discover the meaning by thinking subjunctively.  In Lojban, preface
your utterance with {da'i}, as in

    .i da'i ja'a go'i

With {da'i} you can (attempt to) discover the meaning; then use the
usual tools to (attempt to) determine whether that meaning is true or
false or some degree in between or not determinable.

Two other useful Lojban cmavo for this context:

    la'a        probability; can also be used with numbers for degrees
                of probability with the conventional operations for
                probability.

    ju'o        certainty; can also be used with numbers for scales of
                certainty (what AI programmers call `certainty
                factors').  The mathematical operations for certainty
                scales work quite differently from probabilities, and
                are not yet widely used.

Use uncertainty factors when you don't know truth and don't expect to
find out directly, but have judgements, the results of which you might
test and assign as probabilities.  For example, many species of
mushroom where I grew up are poisonous.  My father often said words to
the effect that `I am fairly certain that is an non-poisonous
mushroom, so we should pick it and take it home; but we should also
make a spore print so as to assign a reliable probability to our
identification.'