Part I: Mill’s Methods redux
Part II: Analogical Reasoning
Homework
• Informal Fallacies
• pp. 103-105, §4.1 “Fallacies in General”
• pp. 121-131, §4.3 “Fallacies of Weak Induction”
• Review:
– Induction
» Analogical Reasoning, e.g., ex. 8.4
» Causal Argumentation, e.g., 8.3b
» Inductive Generalization, e.g., 8.2b
A causal conclusion is strong to the degree that it is
supported by premises
evidence of one or more
Mill’s with
Methods
of Mill’s methods (p. 79)
1. Agreement
2. Difference
Typically establishes
sufficient conditions
– (Agreement & Difference)
3. Concomitant Variation
Establishes variable
relations
4. Residue
Establishes partial
causation
Mill's Method: Concomitant Variation
• Concomitant Variation
– A first discovery: the volume knob
– If variations in phenomenon E coincide with
variations in phenomenon P, then it is probable
that E and P are causally related. (p. 75)
Mill’s Methods: Residue
Characteristic features
1. Deals with complex phenomena
2. Established knowledge of some causal factors
a)
in measured quantities
Subtract from any phenomenon such part as is
known by previous inductions to be the effect of
certain antecedents, and the residue (i.e., remaining
parts) of the phenomenon is the effect of the
remaining antecedents
Mill’s Method: Residue
After realizing a loss of $100,000 a
department store’s chief accountant could
suggest only three causes: an excessive
number of clerks, increases in utility rates,
and damage to merchandise caused by a
flood. These expenses were estimated at
$25,000, $30,000 and $10,000 respectively.
Since no other ordinary sources could be
found, the accountant attributed the
remaining $35,000 to shoplifting.
Mill's Method: Residue
After realizing a loss of $100,000 a
department store’s chief accountant could
suggest only three causes: an excessive
number
of clerks,
increases
in utility
rates,
Is there sufficient
evidence
for this
attribution?
and damage to merchandise caused by a
flood. These expenses were estimated at
$25,000, $30,000 and $10,000 respectively.
Since no other ordinary sources could be
found, the accountant attributed the
remaining $35,000 to shoplifting.
Fallacious: weak induction
Induction – Final Unit
ANALOGICAL REASONING
Analogical Reasoning
• Reasoning that depends on a comparison
– Typically two things, i.e., events, states of affairs,
practices, etc.
Point of Comparison
Common Properties
Inferred
Property
Analogical Reasoning
Analogical Reasoning
Factors Affecting Strength
1. Common features relevantly similar to inferred
feature
a) Number (extent) of these similarities
i.
Diversity among common features
2. No relevant dissimilarities (disanalogy)
Analogical Reasoning
Factors Affecting Strength
1. Relevance of similarities to inferred feature
– Causal connection:
• I’m allergic to hornet stings. Their venom causes me to
swell up and sometimes I come close to losing
consciousness. Yellow jackets aren’t as aggressive as
hornets, but they’re both stinging bees and have a
similar venom. I’ve not been stung by a yellow jacket.
Nevertheless, I’ll keep away from it. I’m probably
allergic to its sting as well.
–
–
–
–
Subject: Yellow Jacket stings
Analogue: Hornet stings
Common features: stinging bee, wasp family, venom
Inferred feature: allergic reaction to venom
Analogical Reasoning
Factors Affecting Strength
1. Relevance of similarities to inferred feature
– Statistical connection:
• Large classrooms like Memorial Hall traditionally have
attendance rates at less than 50% of total. This is, in
fact, especially true of the freshman/sophomore
classes, and classes that meet early in the morning.
Logic 120, a class typically taken by lower classmen, is
also held in a large classroom in the student center
early in the morning. I suspect that this class also has a
low average attendance as well, likely below 50%.
–
–
–
–
Subject: classroom in Student Center (attendance)
Analogue: Memorial Hall (attendance)
Common features: frosh/soph class, meeting time
Inferred feature: low attendance
Analogical Reasoning
Factors Affecting Strength
1. Relevance of similarities to inferred feature
– Aesthetic similarity:
• I enjoy Stephen King’s novels. They are quick, easy
reads but really gripping horror stories. He’s coming
out with a new book, and I think it will be good too.
– Subject: Stephen King’s new book
– Analogue: his previous novels (horror stories)
– Common features: authorship, genre
» “quick and easy,” “gripping”
– Inferred feature: quality of the work (enjoyment)
Analogical Reasoning
Factors Affecting Strength
2. Disanalogies
– A dissimilarity between subject and analogue is
relevant to the inference
• Differences of kind
• Feature possessed by analogue but not subject
Though Jones tends to struggle with his class work, he is a good student in art class.
His random-abstract learning style seems suited the subject. You know, I just noticed
that he has logic right after art class. So I think he’ll do well in logic also.
Comparable Entities?
Dog?
My dog
Argument
Both my dog and my neighbor's dog are wellloved members of the family. Each one is well
fed, house broken, walked on a regular basis.
My dog has a very calm temperament. So I
infer that my neighbor's dog also has a calm
temperament.
Homework
• Informal Fallacies
• pp. 103-105, §4.1 “Fallacies in General”
• pp. 121-131, §4.3 “Fallacies of Weak Induction”
• Review:
– Induction
» Analogical Reasoning, e.g., ex. 8.4
» Causal Argumentation, e.g., 8.3b
» Inductive Generalization, e.g., 8.2b