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From: jiml@cavell.UUCP (Jim Laycock)
Newsgroups: talk.origins
Subject: The LIFE challenge
Message-ID: <900@cavell.UUCP>
Date: Sat, 20-Sep-86 19:59:38 EDT
Article-I.D.: cavell.900
Posted: Sat Sep 20 19:59:38 1986
Date-Received: Thu, 25-Sep-86 00:27:49 EDT
References: <45500088@uiucdcs>
Reply-To: jiml@cavell.UUCP (Jim Laycock)
Organization: U. of Alberta, Edmonton, AB
Lines: 54

In article <45500088@uiucdcs> tullis@uiucdcs.CS.UIUC.EDU writes:
>	So, I challenge anyone who reads this notesfile to the following
>challenge. The challenge is:
>
>		What is LIFE?
>
>	Some things are definitely alive (I am, and you presumably are if
>you are reading this). But how do we definitely draw the line between life
>and non-life? What properties does a system have to have to be A LIVING
>ORGANISM?

LIFE is a vague term, as are so many words in our language.  We have to
approach defining the term from two angles: the intensional (as you suggested,
listing the properties shared by LIVE things), and the extensional (listing
those instances of things we would like to consider ALIVE that do not fall
under our intensional definition).

[Short digression:  CHAIR is equally difficult to define.  How can we
explain to someone the concept that we use to denote office_chairs,
wheelchairs, bean_bag chairs, park benches, electric chairs, and even tree
stumps?  If we provide a simple functional explanation {a chair is a
man-made object that people sit on}, we leave open the possiblity that
tables, or other objects upon which we can sit might also be chairs.
The term CHAIR must intentionally be left vague to fall in line with our
common-sense usage of the word.  End digression.]

Just as there are objects that are, without question, "chairs", there are
systems that are unquestionably alive.  The ~~FUZZY~~ edges of LIFE
can be found at the birth and death of the definite cases:
 
  1. Is a fetus alive?
  2. Is a brain-dead person alive?

and at the border-line between the definite and indefinite cases:
 
  3. Is a virus alive?
  4. Is a complex computer system alive?

Our intuitions with respect to the above 4 questions should influence how
we define LIFE in the general case.  If you believe, as I do, that there
is no single point at which something jumps from NON-LIFE to LIFE, or
vice versa, then you hold that LIFE is a vague term, the ~~FUZZY~~ edges
to which have NO CLEAR CHARACTERIZATION as to whether they are LIFE or
NON-LIFE.  Can something be ~~MORE ALIVE~~ than something else?  Is there
a continuum along which this relation can hold?  When does a foothill
become a mountain?
 
-- 
  Jim Laycock
  decvax!bellcore!ulysses!mhuxr!mhuxn!ihnp4!alberta!cavell!jiml
    OR
  alberta!Jim_Laycock@UQV-MTS
 
  Philosophy major, University of Alberta (5th year)