Hi Alex, (01)
The Okavango is a river in South Western Africa that does not flow in to
the sea or into another river. Instead it finishes in the Okavango Delta
in Botswana, where it flows out into the Kalahari desert in a set of
smaller and smaller branching streams (somewhat like the Nile Delta)
until the smallest streams simply evaporate into the heat. (02)
On Google Maps, a search on "Maun Botswana" will take you to the nearest
town, zoom out and you will see a river delta in the desert. (03)
Therefore, where it flows into is not a vital part of the definition of
what it is to be a river. It might be a vital part of the definition of
the two different French concepts that are similar to the English word
River (one of these flows into the sea, the other into another river),
but then those French concepts would not be able to encompass the
Okavango. Indeed we see that even within one language such as English,
different regions of the world throw up different geographical features
that the mother language never encountered in its own country. For
example the Southern African English word Donga (a seasonal watercourse,
usually in a deep channel) covers the same meaning as what in the Arab
world is called a wadi. Because English borrows words, wadi is also an
English word - but it is synonymous with donga. It is also similar to
the American English creek, though I believe that is expected to have
water in it (I'm not sure, I'm not a native speaker of American!) (04)
As to the parts, I would say that a part of a river called a stretch is
a thing one would want to define. But that does not mean that the
property of having a stretch is a necessary condition of what it is to
be a river. Stretch is an unusual one because to me it seems to be a
more or less human construct for describing sections of a river, so that
stretches can be wherever the person referring to them wants to define
their extent. Rather like a geographical area. So for example I can talk
about the stretch of the Thames from Putney to Mortlake (where the
annual Oxford - Cambridge boat race is held, so there is a reason to
refer to it), but I can also talk about the stretch from Mortlake to the
Thames Barrier (which subsumes the previous stretch) or from Hammersmith
to Barnes (which is within it) or from Hammersmith to Vauxhall (which
overlaps it). More usefully I can refer to the tidal stretch (from
Teddington to ... where does the Thames become the sea?). Or the stretch
from Oxford (way upstream from the rest) to the sea. (05)
This is why I think the Protege model that was shown is mistaken in
trying to make something (the stretch) a part of the definition of what
it is to be a river, when that thing is arbitrary and capable of
infinite varieties of definition. The stretch of a river is not a part
of the river in the way that a part of a pump is a part of a pump. If
one were to try to bodge this in some way, one would at least have to
define a minimum unit in which stretches can be measured. Otherwise,
like the coastline of Britain, it would be infinite. (06)
So I would suggest that a part of something may or may not be a necceary
part of the definition of what it is to be that thing. However, one
should distinguish between arbitrary human descriptions that range over
a thing, and interconnected parts that are themselves coherent things
like washers, impellers and the like. I guess this impinges on the
earlier conversation about systems, in that a river is not a system of
stretches, whereas a pump is a system of pump parts. (07)
Александр Шкотин wrote:
> According to that definition the Okavango is not a river.
> I think it's better to ask the author of definition. If you see
> Okavango as a counterexample.
> I can do it, but I don't know Okavango;)
> Anyway there is a chance to make definition better, or to get more
> about a topographical point of view;)
> So it is a good example around the issues. Are stretches really "Parts"
> of a river for example?
> I guess it's possible to set out too many characteristics of something,
> rather than just those things which, by virtue of being true of an
> individual, make it a member of that class of thing.
> You are right about "characteristics", but parts are very important,
> and for many artificial (and simple natural) things they give definition.
> This is the case with some mixtures of molecules we buy to eat
> (sometimes they wrote these parts on the envelope;) and all
> thechnological things, when we define a thing (or process)
> independently or as part of.
> Have a look at definition in "description" field for "pump":
> and eliminating unnecessary loops...:
> "A physical object that is a driven piece of equipment in which energy
> is either constantly or periodically added to an amount of liquid in
> order to increase the pressure required for the process of moving
> liquid in determinate direction."
> Do we have a formal language for this kind of statements? - Yes and
> not one. For ex. RDF may syntactically "eat" everything, especially
> with reification technique.
> Do we have inference rules (may I say "Figures of the Syllogism";) for
> this language to prove this kind of lemma: "Pump P1 cannot lift water
> on 10 meters."?
> - I don't know. But on my knowledge, DL-reasoner, for ex., has only
> two services: subsumption checking and to check belongness.
> Then we need a lot of logical axioms to reduce different kind of
> inference rules to these two services.
> Well, in math-logic modus ponens is enough somehow. But it more
> reminds Sheffer operation.
> So, where Linguist stops with all broadly used meanings discovered and
> defined, Logician begins clarifying definitions and discovering axioms
> and inference rules.
> what do you think?
> But back to "river".
> for me informal definition as #1a at
> " a natural stream of water of usually considerable volume."
> sound valuable to begin with, but we just should keep in mind that
> usually informal definitions are overlaped.
> like with this one (following m-w.com <http://m-w.com>): brook =
> creek#2 == "a natural stream of water normally smaller than and often
> tributary to a river"
> But good news is that a number of sub-definitions about natural stream
> of water is fixed and small;)
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