PHI 1101: Lecture 8 Oct 18th
Txtbook Chapter 7
The world around us is a really messy web of causes and effects. Yet we seem compelled to try to
What causes cancer?
What made me wear this shirt today?
Why are there this many/few people in class today?
Answers to questions like these, involve makcausal claims .
A causal claim is an assertion about the cause of something.
A causal argument justifies, or supports, such a claim.
Testing for Causes
John Stuart Mill (1806–1873) devised some methods for evaluating causal arguments.
‘Mill’s Methods’ are really just common sense, and they are common in testing scientific theories. 1. Method of Agreement
If two or more occurrences of some phenomenon have only one relevant factor in common, that factor must
be the cause.
The method of agreement involves comparing situations in which the same kind of event occurs. If
the presence of a certain factor is the only respect in which the situations are the same (that is, agree), then
this factor may be identified as the cause of the event.
Imagine three people in your residence all feel sick one night.
All ate at different restaurants; hung out with different people, worked out at different gyms . . .
but all took sips from ONE bottle of water.
If that waterbottle is the one factor they all have in common . . .
then it’s reasonable to conclude that that waterbottle was the cause of their illness.
The Form of the Method of Agreement:
If we’re trying to explain effect ‘E’ . . .
Instance 1: Factors a, b, c are followed by E.
Instance 2: Factors a, c, d are followed by E.
Instance 3: Factors a and c are followed by E.
Instance 4: b and c are followed by E.
Therefore, factor c probably causes E. Only one factor—namely, c—consistently accompanies the effect E.
Conclusion: c likely causes E.
2. Method of Difference
The relevant factor that is present when the phenomenon occurs, and absent when it doesn’t occur, is likely
The method of difference involves comparing situations in which an event of interest occurs with
similar situations in which it does not. If the presence of a particular factor is the only difference between
two kinds of situations, that factor may be said to be “the cause” of the event.
Look for the cases that are different
What’s missing in those cases?
Six players on the team are playing well; three others are not.
The ones not playing well missed a practice last week.
If missing practice is the only relevadifference , then that’s probably the cause.
The Form of the Method of Difference:
Instance 1: Factors a, b, c are followed by E.
Instance 2: Factors a, b are not followed by E.
Therefore, factor c is probably the cause of E. 3. Joint Method of Agreement and Difference
Both the method of agreement and the method of difference combine the two previous reasoning patterns.
The Joint Method of Agreement and Difference involves the simultaneous application of the
previous two methods. We compare cases in which an event of interest occurs with ones in which it does
not occur. The cause of the event will be the only factor present in each case in which the event occurs
and absent in each case in which the event does not occur.
This increases the chances that our conclusion is right.
The likely cause is isolated when you:
Identify relevant common factors that are observed in various occurrences of E
Discard any that are present when there is NO occurrence of E
Imagine that dozens of people stop into a local bar after work as they usually do and that ten of them come
down with an intestinal illness one hour after leaving the establishment. What caused them to become ill?
We can apply the Joint Method of Agreement and Difference to this scenario. Say that among
the ten patrons who become ill, the common factors are that they all drank from the same bottle of wine and
they all had free tacos. So we reason that the likely cause is either the wine or the tacos. After further
investigation, though, we find that other patrons who ate the tacos did not become ill. We conclude that the
wine is the culprit.
We can see how this method (the Joint Method of Agreement and Difference) is at work in
modern controlled trials to the test the effectiveness of medical treatments.
In these experiments, there are two groups of subjects – one known as the experimental group; the other,
the control group. The experimental group receives the treatment being tested, typically a new drug. The control group
receives a bogus or inactive treatment (referred to as a placebo).
This setup helps ensure that the two groups are as similar as possible and that they differ in only one
respect – the use of genuine treatment. A controlled trial, then, reveals the relevant factor common to the
occurrence of the effe