Informal logic Paweł Łoziński Informal...

Pawe ozi skił Ł ńInformal logic

11/03/2008 1

Informal logic

Paweł Łoziński

Institute of Computer ScienceFaculty of Electronics and ITWarsaw Univ. of Technology

e-mail: [email protected]: http://www.ii.pw.edu.pl/~plozinsk

mailto:[email protected]


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Agenda

Historical background

Informal logic

Trials of informal logic formalization

Fallacies

Conclusions


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Logic

Questions that brought logic into being:

How do we reason?

How do we justify our convictions?

Logic was born as a study of (not necessarily effective) proper reasoning.

Focus on reasoning itself, not things we reason about.


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Foundations

Stephen Toulmin. The uses of argument. 1958

Arthur Hastings. A reformulation of the modes of reasoning in argumentation. 1963

Charles Hamblin. Fallacies. 1970


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,,Birth”

The 70s of the XXth century

Ralph H. Johnson, John A. Blair. Logical self-defense. 1977:

Reasoning that doesn’t feature certainty (e.g. analogy); it’s based on the content of thestatements being made.


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How do we reason?

Sample inferences:

„John says chances for rain are about 75%”,

„Allowing stem cell research is playing God”,

„Polish economy will develop similarly to Ireland's few years ago”.


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Informal logic - features

Uncertainty:

we cannot guaranty that claim inferred from true premises will be true,

we cannot guaranty that claims thought to be true won't be falsified when new facts arrive.

Dialogue is:

a method of verification claims truthfulness,

a context for evaluation of soundness of inferences.

Language dependant: validity of our reasoning depends on the words we use to express it.


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What is truth in informal logic?

We consider a claim truthful, if given the current state of knowledge the assumption that the claim is true

is more rational, than assumption that it's false.

How do we decide what is more rational?

Through dialogue.


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Premises

Argument structure(Stephen Toulmin, 1958)

Claim

Premises

Warrant Inference

Context

Premises


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Example

U.S.A. should ratify the Kyoto Protocol.

- Germany has reduced greenhouse gas emissions by 17.2% in years 1990-2004 as an effect of ratification of the Kyoto Protocol.

- U.S.A. didn't ratify the Kyoto Protocol.

Things that are generalyalike will be alike in

a given aspect. Inference

1. We accept arguments from analogy.

2. Reducing greenhouse gas emission is a good thing.

3. We accept causal relation in the case of Germany.


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Premises


Claim

Premises

Warrant Inference

Context

Premises


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Claim

Claims can be contradictory on 4 different levels:

level of fact,

level of definition,

level of value,

level of policy.


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Premises


Claim

Premises

Warrant Inference

Context

Premises


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Premises

Premise is data that critical audiences generally accept.

What can be a premise?

Objective data – statistics, experiment results, items (e.g. in a court case).

Generally accepted claims.

An opinion of a credible person (competent, trustworthy, good will, dynamic).

Claims supported by other, valid arguments.

Irrefutable premises don't exist.


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Premises


Claim

Premises

Warrant Inference

Context

Premises


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Rules of inference (argumentation schemes – D. Walton, 1996)

Argument from generalization

Argument form causal relation

Argument from sign

Argument from analogy

.......

....

..

.


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Rules of inference,argument from sign

Warrant: X and Y are likely to coincide.

Often link phenomena from different realms:

„Avoiding eye contact is a sign of insincerely”


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Rules of inference,argument from analogy

Warrant: things that are generally alike will be alike in a given aspect.

Analogy types:

literal (e.g. „Berlin is like London because ...”),

figurative (e.g „Abandoning your studies in order to earn money is like trading an axe for a stick”).


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Premises


Claim

Premises

Warrant Inference

Context

Premises


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Arguments context

A set of presupposed claims (cultural, ethical, social, ...)

Dialogue


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Dialogue

We use uncertain rules of inference, how do we decide whether we are right or wrong?

By testing our claims through process of questions and answers – dialogue.

Examples of dialogues:

everyday discourse,

court trials,

Plato's dialogues.


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Dialogue

Presumption and burden of proof

Commitments


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Dialogue types (D. Walton, E. Krabbe, 1995)


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Dialogue

Dialogue stages:

opening stage (specifying the type and rules of the dialogue)

locution rules

dialogue rules

commitment rules

win-loss rules

confrontation stage (specifying what's the controversy)

argumentation stage (the main part...)

closing stage (deciding what is the outcome of the dialogue)


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Terms related to informal logic

Argumentation theorymodelling argument's internal structure (e.g. Toulmin)

classifying rules of inference (argumentation schemes),

classifying fallacies.

Dialogue theory

researching general rules that govern dialogues,

researching that makes a productive dialogue.


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Formalization trials

If you can formalize something, you can implement it...


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Logic – definition

Ordered triple of:

language – {chair, red, Birds fly, ...}

semantics – horse Andiamo

inference mechanism – if ... than ...


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In case of informal logic

language – natural language,

semantics – relation between the natural language and the reality,

inference mechanism – arguments.


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What is truth in „formalized” informal logic?

We consider a claim truthful, ifthere exists a winning strategy

in a formal dialogue game where truthfulness of the claim is at stake.

This makes informal logic an instance of dialogue logic (Paul Lorenzen)


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Formal argumentation systems

Argumentation Framework (P. Dung, 1995)

, where:

is a set of arguments,

is a relation of attacking (e.g. argument a attacks b).

The main problem: What conditions does a set of arguments have to satisfy in order to be somebodies point of view?

AF=AR ,attacks

AR

attacks⊆AR×AR


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Argumentation framework

a

f

b

d

e

c


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Argumentation framework

Oriented graph G = (V, E), where:

V is a set o vertices,

E is a set o edges.

In the given example:

V = {a, b, c, d, e, f},

E = { (a,b), (a,c),

(c,a), (c,b), (c, d),

(d,e) }.

a

f

b

d

e

c


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Argumentation framework(some definitions)

A set of arguments is conflict-free if and only if there are no arguments and , such that:

Argument is acceptable with respect to if and only if every argument that attacks is attacked by an argument in .

A conflict-free set is admissible if and only if is acceptable with respect to .

Characteristic function is defined as follows:

a∈S , b∈S , a attacksb

S⊆ARba

S⊆ARaa

S

S⊆ARS

S

F AF S ={a∈AR: a is acceptable wrt S }


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Argumentation framework(some points of view)

A naive point of view is a set of arguments is a maximal acceptable set of arguments.

A sceptical point of view is a minimal set of arguments such that . F AF S =SS


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Argumentation framework(developments)

The relation of support

a

f

b

d

e

c


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Argumentation framework(developments)

More general relation of attacking

a

f

b

d

e

c


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Formal dialogue systems

Prakken's framework (H. Prakken, 2005)

Presupposes existance of a Dung's Argumentation Framework

Comprises of elements:

topic language,

communication language,

protocol,

outcome (win-loss) rules,

commitment rules.


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Prakken's framework(communication language)


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Prakken's framework(PROLOG implementation)


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Fallacies

Argumentum ad hominem (personal attack)

Argumentum ad baculum (resorting to force)

Argumentum ad verecundiam (argument from „modesty”)

bad usage of an argument from expert's opinion.

They are not always fallacies...


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Conclusions

Informal logic is supposed to describe human way of reasoning where:

arguments are inference mechanisms,

dialogue is a method for evaluating claims.

There are formalization trials, but:

its a relatively young and unexplored discipline,

its hard to create objective descriptions of it's components, and therefore hard to formalize.

Informal logic Paweł Łoziński Informal...

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