Expanded Notes on PPAs


Four broad argument categories dominate the PPA landscape: inductive arguments, abductive arguments, arguments by analogy, and confirmation arguments.  Here are thumbnail sketches of each of these, with examples and a description of the standards that distinguish good examples from bad:

  1. Inductive Arguments:  The conclusions of these arguments are generalizations from similar observations or other similar data points, which serve as reasons. 

    • Example: 100,000 people have taken drug X without experiencing any side effects; therefore, drug X has no side effects.

    • Standards

      • Representativeness: The more the observed events fully represent that type of event, the stronger the argument will be; 

      • Number: The greater the number of observations, the stronger the argument will be. 

  2. Abductive Arguments:  The reasons in these arguments present clues, often widely disparate, and the conclusion is the "best explanation" available for these clues. 

    • Example: I lost my keys; they aren't in my car or my backpack; they aren't in the junk drawer or by the phone; they aren't on the mantle place.  Therefore, the only other place they could be is in my gym bag.  (Think of the game Clue here---it is all about generating abductive arguments.)

    • Standards

      • Best Conclusion: The more relevant considerations accommodated by a conclusion, the stronger that conclusion will be. Furthermore, the more apparent relationships between the considerations accommodated by a conclusion, the stronger that conclusion will be.

      • Plausible Alternatives: This assessment is made of the set of alternatives as a whole, and it is highly context-sensitive. What might seem a plausible set to you, given the issue, may well appear narrow and implausible to someone with more imagination or more experience. On the other hand, it may turn out that what all regard as plausible up front turns out to be implausible because every available alternative fails to satisfy a crucial condition and so they must all be rejected. (For example, consider a criminal investigation in which all the suspects have solid alibis.) Or perhaps in the course of assessing the alternatives, new information comes to light, pointing the way to new and different alternative conclusions. The important thing here is to remember this dimension of analysis—the best car from a bad lot is still a lemon.

  3. Arguments by Analogy: The conclusion about one issue is supported by reasons the point out how a different but structurally similar issue generates a similar conclusion.

    • Example: My friend argues that he takes good care of his dog, feeding him, walking him, taking him to the vet regularly.  Thus, he says, he will make a good parent when the time comes.

    • Standards:

      • Plausibility: The more plausible the story, the stronger the argument. 

      • Structural Similarity: The more structurally similar the story in an analogy is to the topic, the stronger the argument formed around this analogy will be.

      • Inferential Strength: The more closely connected the conclusion about the story is to the shared structural elements, the more closely connected the desired conclusion will be to the topic.

  4. Confirmation Arguments: In these, you derive a hypothesis from your theory and then test it; if the observations you make support your hypothesis, then it counts as a confirmed conclusion.

    • Example: If exposure to the sun causes skin cancer, then we should find a higher incidence of skin cancer among those who spend a great deal of time in the sun; we do fin an increased incidence of skin cancer among this population; therefore, exposure to the sun must cause skin cancer.

    • Standards:

      • Strength of Implication: The stronger the connection between background claims and implied hypothesis, the greater the degree of confirmation afforded the background claim given the truth of the hypothesis. 

      • Experimental Certainty: The argument will only be as strong as the degree of certainty associated with the truth value of the hypothesis. 

      • Strength of Conclusion: The more a confirmation argument is asked to confirm, the weaker the confirmation supplied.

For more detail on all of these, see Chapter Six, Section III.3 of the UI Critical Thinking Handbook.