I've been looking for it, but Google leads the search to multiple sort of pages that, although they talk about logic, explain the subject very differently from each other and they don't fix a list with the same items and they usually don't list all of them (some points prediction, generalization, analogy, authority others reductio or even the difference between "then" and "possibly", for example); also, I tried it in the mathematics forum, but they advised me to bring it here in exchange and then I'm doing it in order to achieve a clarification.

So I thought it'd be nice to have this question answered here so that it helps me to clear my doubts now at the same time it helps others in the future as well.

And, in the field of informal logic, what are good examples of the types of non-deductive arguments?

Thanks in advance!

  • 3
    As far as the logical form is concerned, the other two types are induction and abduction. As for the rest, they are types of material arguments, that is arguments depending on the content of what is reasoned about, in addition to form. Hence, they are confined to a restricted content domain, and do not apply universally. Many informal fallacies (analogy, authority, generalization, etc.) are such argument types pushed beyond their domain of applicability.
    – Conifold
    Commented Jun 18, 2019 at 20:46
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    For example inductive arguments are not deductive. I saw humans die in the past, then probably all humans die. I went from particulars to universals, this is induction. Then there is deduction that uses the conclusion of the induction as a premise : all humans die, I am a human, then I will die (this went from universals to particulars).
    – SmootQ
    Commented Jun 18, 2019 at 21:52
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    And then there is abduction : "either I will die, or (science will invent a cure for death AND the earth will not be hit by an asteroid and I will not get involved in a deadly accident AND the universe will go on forever AND humans will migrate to an infinite number of planets....etc) . Using abduction, I can safely conclude that probably (very very likely) I will die and most likely not all those ANDs will be true (I probably will die because one of all those possible ANDs will turn out to be false).
    – SmootQ
    Commented Jun 18, 2019 at 21:57

1 Answer 1


Douglas Walton proposed returning to Aristotle's dialectic as a way to look at arguments:

This new way of viewing an argument is frequently called informal logic, suggesting a contrast with formal logic (the dominant type of logic in western intellectual tradition). But it could also be called communicative logic, or pragmatic logic perhaps, in that it is expressly directed to judging particular aspects of how an argument was used for some communicative purpose, well or badly, in a given case.

Formal logic evaluates an argument by its form. The form has to be valid. Walton claims this is different for an informal argument:

The form is not, by itself, sufficient to enable one to arrive at an evaluation of the argument as weak or strong, reasonable or fallacious....

In informal logic, an argument is evaluated with respect to how it has been used in that particular case, within the framework of what is called a type of dialogue. A dialogue is a goal-directed, collaborative conversational exchange, of various types, between two parties.

If one looks at deductive logic as formal logic and non-deductive logic as informal logic one may be able to use Walton's dialogue types as a way to list the different types of non-deductive arguments. This may not present a fixed list of non-overlapping items that agrees with other lists, but it would provide a basis upon which one could say whether or not an argument, or dialogue, should be placed somewhere in one's grouping of informal, non-deductive arguments.

Walton offers seven dialogue types in the paper:

  1. The "critical discussion" occurs where the goal is to resolve a conflict of opinions.
  2. The "persuasion dialogue", broader than the critical discussion, occurs where one side attempts to prove a thesis using premises accepted by the other side.
  3. The "negotiation type of dialogue" occurs where the goal is to make a deal.
  4. The "quarrel" occurs where the goal is a better personal relationship between the parties.
  5. The "information seeking type of dialogue" occurs where the goal is to transfer information from one party to another.
  6. The "deliberation" occurs where two parties are trying to decide what action to take when prompted by a practical problem.
  7. The "inquiry" occurs where the goal is to prove something to a high standard.

This list looks different from a list of informal fallacies of relevance or ambiguity or a discussion on analogy, probability and scientific hypothesis as a contrast with deduction that one finds in logic textbooks such as Irving Copi's Introduction to Logic. Here informal logic is based on its own foundation of dialogue rather than on how it contrasts with deduction's emphasis on valid form.

Copi, I. M. Introduction to Logic. Sixth Edition. Macmillian. 1982.

Walton, D. New Methods for Evaluating Arguments. Inquiry: Critical Thinking Across the Disciplines. Summer. 1996. https://www.dougwalton.ca/papers%20in%20pdf/96NewMethod.pdf

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