Lincoln-Douglas Debate
How to Define your Terms in Lincoln-Douglas
Debate
by George H. Smith
How a
debater defines the key terms in a resolution can seriously
affect the outcome of a debate. How can you arrive at good
definitions when presenting your side? And how can you recognize
the faulty definitions offered by your opponent?
Logicians
generally agree on the basic components of a definition and
on the rules for adequate definitions. A debater who learns
the structure and rules of definition has a significant advantage
over his adversaries. Some aspects of definition are rather
technical, but they will more than repay the time and effort
it takes to master them.
A definition
has three parts: (l) the definiendum, (2) the copula, and
(3) the definiens. We can illustrate these parts with Aristotle's
famous definition "Man is a rational animal."
DEFINIENDUM
COPULA DEFINIENS
Man is
a rational animal.
"Man"
is the word being defined, so it is called the definiendum
(literally,: "the thing to be defined"). The verb "is" links
the subject to the predicate, so it is called the copula.
The phrase "a rational animal" does the work of defining,
so it is called the definiens (literally, "thing which does
the defining").
In addition,
the definiens is subdivided into two parts: (l) the genus,
and (2) the differentia. In Aristotle's definition, "rational
animal" is the definiens. This is divided as follows:
DEFINIENDUM
COPULA DEFINIENS DIFFERENTIA GENUS
Man is
a rational animal.
"Genus"
refers to the general class to which the definiendum ("man")
belongs. Aristotle assigns "man" to the broader class of beings
known as "animal"; thus, "animal" is called the "genus" of
"man."
"Differentia"
refers to the specific difference(s) by which we distinguish
the definiendum ("man") from other members of the genus ("animal").
Aristotle uses the attribute "rational" to distinguish man
from other animals; thus, "rational" is called the differentia
(the specific difference) of "man."
Before
pushing on, we need to discuss one more term: species. A species
is a subclass of a genus. Thus, "man" &endash; a subclass
of the genus "animal" &endash; is said to be a species of
"animal."
"Genus"
and "species" are relative terms, like "parent" and "offspring."
John is a parent in relation to his children but he is also
an offspring in relation to his own parents. In the same way,
"animal" is a genus when compared to the species ''man," but
"animal" is also a species when compared to the genus "living
beings."
Here is
another example: "table" is a genus relative to the species
"dinner table " But "table" is a species of the genus "furniture"
&endash; and "furniture" is itself a species of the genus
"household goods," and so on.
Now, having
armed ourselves with the rudiments of definition, let's see
how we can arrive at good definitions and spot faulty ones.
1. Definitions
should not be too broad.
A definition
is too broad if the definiens includes more items than it
properly should. For example, consider this definition: "A
circle is a figure all of whose points are equidistant from
a given point."
A little
reflection will reveal the inadequacy of this definition.
The definiens includes not only circles, but arcs and spheres
as well. Hence our definition is too broad.
The definiens
needs to be recast. But how? The definiens, as we know, consists
of two parts: the differentia and the genus. Let's glance
at each of these.
The differentia
("all of whose points are equidistant from a given point")
is adequate, but the same cannot be said for the genus ("a
figure"). This is too broad, because it admits arcs and spheres.
So let's try a more restricted genus: "a closed, plane figure."
This genus excludes arcs and spheres and so accomplishes our
purpose. Our definition is now adequate and may be broken
down as follows: "A circle" (the definiendum) "is" (the copula)
"a closed, plane figure" (the genus) "all of whose points
are equidistant from a given point" (the differentia).
2. Definitions
should not be too narrow.
A definition
is too narrow if the definiens improperly excludes some items.
Consider this definition: "A thief is a person who steals
money" Clearly, this definition is too narrow, because some
thieves steal other things than money.
In this
example, the problem lies with the differentia ("who steals
money"). This is too restrictive. The word "money" should
be eliminated, thereby leaving us with an adequate definition:
"A thief" (the definiendum) "is" (the copula) "a person" (the
genus) "who steals" (the differentia).
Some definitions
are both too broad and too narrow, as we see in this example:
"A novel is a prose narrative about people." The genus ("prose
narrative") is too broad, because it does not rule out short
stories, etc. In addition, the differentia ("about people")
is too narrow, because it rules out narratives about animals,
robots, etc.
3. The
definiens should apply to ALL possible instances of the definiendum
and ONLY to those instances.
To apply
this rule to Aristotle's definition of man, we need to ask:
Are all men rational, and are only men rational? Logicians
call this the "all and only test"
This is
an easy way to detect definitions that are too broad, too
narrow, or both. Let's illustrate this test with some faulty
definitions presented earlier:
(a) "A
circle is a figure all of whose points are equidistant from
a given point."
Is this
true of all circles? Yes. Is this true only of circles? No.
This definition fails the "only" part of the test; it is too
broad.
(b) "A
thief is a person who steals money."
Is this
true of all thieves? No. Is this true only of thieves? Yes.
This definition fails the "all" part of the test. It is too
narrow.
(c) "A
novel is a prose narrative about people."
Is this
true of all novels. No. Is this true only of novels. No. This
definition fails both parts of the test; it is at once too
narrow and too broad.
4. The
differentia should state the ESSENTIAL characteristic of the
definiendum.
Some definitions
pass the "all and only test," but they fail in another way:
they do not state the essential characteristic of the definiendum.
Consider these definitions:
"Man is
an animal that can (has the capacity to) build computers."
"Man is
an animal that can (has the capacity to) build automobiles."
These
definitions pass the "all and only test." But their differentia
&endash; the capacities to build computers and automobiles
&endash; do not identify the essential characteristics of
man. In other words, these characteristics are not fundamental
or basic to what is meant by the concept "man."
An essential
characteristic is that characteristic which best explains
or accounts for the definiendum's other characteristics. Man's
ability to build computers, in itself, does not explain his
ability to build cars. Nor is the reverse true.
Now consider
Aristotle's definition. "Man is a rational animal" Man's rationality
(i.e., his capacity to reason) accounts for his ability to
make computers, cars, and many other things. Thus, we can
say that rationality is essential to the concept "man " "Rational"
is the proper differentia to distinguish man from other animals.
5. Definitions
should not be circular.
This rule
is fairly obvious. The definiens should not use the word being
defined, or some variant of it. Here are two examples of circular
definitions:
"A line
is a linear path."
"A carpenter
is a craftsman who practices carpentry."
6. Definitions
should avoid metaphorical and figurative language. They should
be literal.
"A camel
is the ship of the desert." "The lion is the king of beasts."
Definitions should avoid this kind of language.
Philosophers
sometimes commit this error when they define the State as
an organism. For example, in Leviathan (1651), Thomas Hobbes
defines the State as "an artificial man . . . in which the
sovereignty is an artificial soul, as giving life and motion
to the whole body."
7. Definitions
should not be vague, obscure or ambiguous.
This rule
serves the interest of clarity, and the value of clarity should
be apparent to all debaters.
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