The Language of Argument

2 8 1

sl i p p e r y sl o p e s

significant difference. U.S. Senator Everett Dirksen put the point memorably

when he said, “A billion dollars here and a billion dollars there can add up

to some real money.” To the extent that conceptual slippery-slope arguments

depend on this questionable assumption, they provide no more support for

their conclusions than do arguments from the heap.

Unlike arguments from the heap, however, conceptual slippery-slope

arguments do often lead people to accept their conclusions. Slippery-slope

arguments have been used to deny the difference between sanity and insan-

ity (some people are just a little weirder than others) and between amateur

and professional athletics (some athletes just get paid a little more or more

directly than other athletes). When many small differences make a big differ-

ence, such conceptual slippery-slope arguments are fallacious.

This fallacy is seductive, because it is often hard to tell when many small

differences do make a big difference. Here is a recent controversial example:

Some humans have very dark skin. Others have very pale skin. As members

of these different groups marry, their children’s skin can have any interme-

diate shade of color. This smooth spectrum leads some people to deny that

any differences among races will be important to developed theories in biol-

ogy. Their argument seems to be that the wealth of intermediate cases will

make it difficult or impossible to formulate precise and exceptionless laws

that apply to one racial group but not to others, so differences among races

will play no important role in sciences that seek such laws. Critics respond

that some scientific laws about races still might hold without exception even

if skin color and other features do vary in tiny increments.

Whichever side one takes, this controversy shows that, even if there is a

smooth spectrum between end points, this continuity is not enough by itself

to show that there are no scientifically significant differences among races.

That conclusion would need to be supported by more than just a concep-

tual slippery-slope argument. To show that certain concepts are useless for

the purposes of a certain theory, one would need to add more information,

particularly about the purposes of that theory and its laws. That is what de-

termines which differences are important in that particular area. Conceptual

slippery-slope arguments might work in conjunction with such additional

premises, but they cannot work alone.

Whenever we find one thing passing over into its opposite through a gradual

series of borderline cases, we can construct (a) an argument from the heap and

(b) a conceptual slippery-slope argument by using the following method: Find

some increase that will not be large enough to carry us outside the borderline

area. Then use the patterns of argument given above. Applying this method,

exercise III

(continued)

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