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Jeffrey Lotz jlotz at medea.gp.usm.edu
Fri Feb 17 17:01:15 EST 1995

M. Siddal makes an interesting and germane point about 
definitions of parasite. But in my opinion goes to far or at 
least does not complete the discussion. His conclusion that a 
parasite is whatever a parasitologist studies is similar to the 
definition of a species as "whatever a competent taxonomist 
says". I think the outlook is brighter for the reality of the 
parasitic mode of existence than that. 

Nonetheless his comments go to the heart of defining and 

Words are different than the things they refer to. Some words 
refer to "natural" things and some refer to human constructs. I 
don't know how one can tell the difference with any certainty. 
However, it does suggest that there are at least two kinds of 
words (nouns) therefore two kinds of approaches that can be 
taken to arrive at a definition. One is to define words by 
convention. The other is to define words by inspection. These 
two ways have much in common with the analytic/synthetic 
distinction of Kant. Definitions by convention are about human 
constructs. Definitions by inspection are about "real" objects 
(in some sense). I realize this distinction may not hold 
completely (cf. W.V.O. Quinne's Two dogmas of empiricism). 
Nonetheless it helps when considering definitions.  

A definition by convention is arrived at by agreement of what a 
"word" will stand for. If it is decided that "chair" stands for 
any nonliving thing used to sit on, that has four legs and a 
back. Then stools are not chairs. If prevalence is defined as 
the proportion of animals infected then that is it. If a 
community is defined as a set of interacting species then that 
is it. There is no need for discussion because the issue is not 
understanding these things it is about communication. In fact 
things that are defined this way are unlikely to be "real 
things", just human constructs.    

On the other hand a definition by inspection is arrived at only 
after a thorough analysis of the things themselves. For the 
chair example, one points to things that are "chairs" then 
determines what is common to all of those things and attempts 
to distill the commonalities. One might learn something new 
about chairs, e.g., that they all don't have four legs.

The process of arriving at a definition  of "parasite" ^M
might be to begin ^M
with examples of what would be universally considered parasites, 
i.e., things studied by parasitologist or that are covered in 
text books on parasitology. However, I would not want the 
process to stop there. It seems that if parasites are "real 
kinds" of things then we might learn something about parasites. 
Maybe we would find that there are organisms that are parasites 
eventhough they are not studied by those that call themselves 
parasitologists, e.g., virologists.

Jeffrey M. Lotz                     Phone (601) 872-4247
Gulf Coast Research Lab             Fax   (601) 872-4204
P.O. Box 7000                       Internet: jLotz at medea.gp.usm.edu
Ocean Springs, MS 39566-7000 USA

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