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Types of Argumentation
Critique of Induction

Inductive arguments can be divided into four kinds, depending on two factors. The factors are...

     (1) the sample - which can be either...
               (a) simple (uncontrolled); or
               (b) bifurcated (controlled)

     (2) the nature of the generalization - which can be either
               (a) straight (to the population as a whole); or
               (b) oblique (to other unobserved cases within the population).

These two factors create a grid with four quadrants.

 

 
 
  Simple (uncontrolled) sample    Bifurcated (controlled) sample   
 

 

Straight generalization
  Uncontrolled studies that
  generalize to an entire population.

EXAMPLE:

Opinion polls
 

 
  Controlled studies that
  generalize to an entire population.

EXAMPLE:

Comparison studies
(e.g. comparing
 women to men)
 
 

 

Oblique generalization
   Arguments from observed
   cases to unobserved cases.

EXAMPLE:

Analogical arguments;
trend projections

 
   Controlled studies applied
   to new individual cases.

EXAMPLE:

Medical studies
 

 

 

 
There are five criteria by which Inductive arguments should be evaluated. However, only the first three criteria apply to every sort of Inductive argument. The fourth criterion applies only to oblique generalizations and the fifth criterion applies only to arguments based on a bifurcated sample.

 
I. Sample Size

The larger the sample, the stronger the induction. For example, a study done on 100 subjects is generally stronger than a study done on only 10.

 
II. Diversity of Sample

The more points of difference among the members of the sample, the stronger the induction. For example, an opinion poll must include subjects with wide variation in geography, age, race, religion, political affiliation, income, etc.

 
III. Decisiveness of the property being observed

The more clear and decisive the property appears in the sample, the stronger the induction. Vice versa, being modest in our statement of the conclusion can also strengthen the induction. For example, claiming to have evidence of life on Mars is much more modest than claiming to have evidence of intelligent life.

 
IV. Similarity of the sample to the unobserved cases (Oblique generalizations only)

The more points of similarity, the stronger the induction. For example, to draw conclusions about human anatomy (without actually dissecting a human), it would be better to dissect a chimpanzee than a tree.

 
V. Comparability of the experimental group to the control group (Controlled samples only)

The more points of comparison, the stronger the induction. For example, in a drug safety study, if the experimental group is made up of young women, the control group must also be made up of young women, to ensure that age and sex differences are not responsible for observed differences between the groups.

 

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