The Language of Argument

2 2 9

A p p l y i n g T h e s e M e t h o d s t o fi n d C a u s e s

These reflections suggest the following contextualized restatement of our

original definitions of sufficient conditions and necessary conditions:

F is a sufficient condition for G if and only if, whenever F is present in a

normal context, G is present there as well.

F is a necessary condition for G if and only if, whenever F is absent from

a normal context, G is absent from it as well.

What will count as a normal context will vary with the type and the aim

of an investigation, but all investigations into causally sufficient conditions

and causally necessary conditions take place against the background of

many factors that are taken as fixed.

Background Assumptions

If we are going to subject a causal hypothesis to rigorous testing with the

SCT and the NCT, we have to seek out a wide range of cases that might

refute that hypothesis. In general, the wider the range of possible refuters

the better. Still, some limit must be put on this activity or else testing will

get hopelessly bogged down. If we are testing a drug to see whether it will

cure a disease, we should try it on a variety of people of various ages, medi-

cal histories, body types, and so on, but we will not check to see whether it

works on people named Edmund or check to see whether it works on peo-

ple who drive Volvos. Such factors, we want to say, are plainly irrelevant.

But what makes them irrelevant? How do we distinguish relevant from

irrelevant considerations?

The answer to this question is that our reasoning about causes occurs

within a framework of beliefs that we take to be established as true. This

framework contains a great deal of what is called common knowledge—

knowledge we expect almost every sane adult to possess. We all know,

for example, that human beings cannot breathe underwater, cannot walk

through walls, cannot be in two places at once, and so on. The stock of these

commonplace beliefs is almost endless. Because they are commonplace

beliefs, they tend not to be mentioned; yet, they play an important role in

distinguishing relevant factors from irrelevant ones.

Specialized knowledge also contains its own principles that are largely

taken for granted by experts. Doctors, for example, know a great deal about

the detailed structure of the human body, and this background knowledge

constantly guides their thought in dealing with specific illnesses. Even if

someone claimed to discover that blood does not circulate, no doctor would

take the time to refute that claim.

It might seem close-minded to refuse to consider a possibility that some-

one else suggests. However, giving up our basic beliefs can be very costly. A

doctor who took seriously the suggestion that blood does not circulate, for

example, would have to abandon our whole way of viewing humans and

97364_ch10_ptg01_215-238.indd 229 15/11/13 10:48 AM

some third party content may be suppressed from the eBook and/or eChapter(s). Editorial review has deemed that any suppressed content does not materiallyCopyright 201^3 Cengage Learning. All Rights Reserved. May not be copied, scanned, or duplicated, in whole or in part. Due to electronic rights,

affect the overall learning experience. Cengage Learning reserves the right to remove additional content at any time if subsequent rights restrictions require it.