Principios de Taxonomia

3.5 Artificial Classes and Natural Kindsj55
Some possibilities for selection are noticeably subjective because they reflect
nothing but personal taste, such as the class of ugly looking worms (Ghiselin, 2002).
Other group formations that are made according to trait resemblance are suspected
of being purely human-made. These are the class formations that are based on traits
that are objectively measurable in nature; for example, formations of items that
have the same color are grouped into a common class: the class of red objects. Such
classes may be assumed to exist in reality, though the question of reality is disputed
here (Riggs, 1996). There are divergent opinions about whether a class of red items
really exists or whether these classes are also figments of the human mind that only
serve communication with fellow human beings (Goodman, 1956; Armstrong,
1978). The author of this book supports the view that a class of red objects is not a
naturally preset entity but a mental construct although, of course, the red objects
are natural.
The correlation of class formation with natural causes or laws is crucial for the
question of whether classes are natural or human fiction. There are obviously
artificial classes that serve the human need for order and mutual communication,
and these are obviously not discovered but made. Such artificial classes do not exist
outside of our minds. Only the members of the class exist, but the classes
themselves do not exist as natural groups (Devitt, 1991). For example, an artificial
class would be the group of all objects whose names begin with a D. Charles
Darwin,theextinctDodoandallducksformacommonclassaccordingtothis
criterion. Without a doubt, the class of all German citizens that were born on May
1st 1990 is an artificially made class.
The class of bearded men is also an artificial class because no natural law is broken
or disregarded if a member of the class shaves and becomes be excluded from the
class (Ghiselin, 1997). Only the human principle of order forbids the continued
treatment of the shaved individual as a member of the class of bearded men.
However, the principle of order is not a natural law; the group of bearded men is
an artificial construct that does not in reality exist in nature.
However, there appear to be classes that are not the result of a human sorting effort
because their class cohesion is based on natural causes or laws. These classes are
called natural kinds (Riggs, 1996). Although natural kinds are classes and are hence
based on trait equality, like the artificial classes, and not on relational connections,
like the relational groups (see above), they are not made by humans.
To make this difference more clear: It is important to distinguish between
nominalistic and realistic classes. Although both are groups of objects whose group
affiliations are based on trait similarity or equality, the former are artificial constructs
whereas the latter are natural. Nominalistic classes are linguistically or mentally
constructed aggregates of objects that are connected by nothing other than the fact
that they fall under a certain predicate or concept (Kripke, 1980; Putnam, 1975; Riggs,
1996). In contrast, natural classes ( natural kinds ) exist independently from our
language and our brain activity and would even exist as groups without humans to
sort them. Realistically understood natural classes are groups that are based on
natural laws. The trait similarities that unite the members of such groups in natural
kinds permit nomological generalizations.