Informal logic - Warsaw University of...

Historical backgroundArgumentDialogueFallacies

Attempts of informal logic formalisationConclusions

Informal logic

Paweł Łozinski

http://www.ii.pw.edu.pl/∼plozinsk

Institute of Computer ScienceFaculty of Electronics and Information Technology

Warsaw University of Technology

17 March 2009

Paweł Łozinski http://www.ii.pw.edu.pl/∼plozinsk Informal logic

Agenda

1 Historical background

2 Argument

Premises

Rules of inference

3 Dialogue

“Justification”

Fundamental concepts

Dialogue stages

4 Fallacies5 Attempts of informal logic formalisation

Some developments – argumentation

Some developments – dialogue

6 ConclusionsPaweł Łozinski http://www.ii.pw.edu.pl/∼plozinsk Informal logic

Agenda

2 Argument

Premises

Rules of inference

3 Dialogue

“Justification”

Dialogue stages

Agenda

2 Argument

Premises

Rules of inference

3 Dialogue

“Justification”

Dialogue stages

Agenda

2 Argument

Premises

Rules of inference

3 Dialogue

“Justification”

Dialogue stages

Agenda

2 Argument

Premises

Rules of inference

3 Dialogue

“Justification”

Dialogue stages

Agenda

2 Argument

Premises

Rules of inference

3 Dialogue

“Justification”

Dialogue stages

Agenda

2 Argument

Premises

Rules of inference

3 Dialogue

“Justification”

Dialogue stages

Ancient Greece – logic

Questions that brought logic into being:

How do we reason?

How do we justify our convictions (what makes a good/bad justification)?

Focus on reasoning itself, not things we reason about.

Sylogism

(. . . ) discourse in which, certain things being stated, something other than what

is stated follows of necessity from their being so.a

aAristotle. Prior analytics, par. 100b; Topics, par. 24a.

How do we reason?

Sylogism

How do we reason?

Sylogism

19th century – formal logic

Characteristic features:

1 Focus on infaliablity of reasoning (deduction).

2 Subject independence.

19th century – formal logic

Characteristic features:

1 Focus on infaliablity of reasoning (deduction).

2 Subject independence.

Informal logic – early fundations

Stephen Toulmin. The uses of argument. 1958.

Arthur Hastings. A reformulation of the modes of reasoning in

argumentation. 1963.

Charles Hamblin. Fallacies. 1970.

Informal logicBack to the question: How do we reason?

Sample bases for reasoning:

“John says chances for rain are about 75%”;

“Allowing stem cell research is playing God”;

“Polish economy will develop similarly to Irish economy few years earlier”.

Informal logic – main 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.

Language dependance: validity of our reasoning depends on the words we

use to express it.

Dialogue:

a method for deciding whether a claim is true or false;

a context for evaluation of our inferences.

Uncertainty:

new facts arrive.

use to express it.

Dialogue:

Uncertainty:

new facts arrive.

use to express it.

Dialogue:

Uncertainty:

new facts arrive.

use to express it.

Dialogue:

ClaimPremisesRules of inference

Agenda

2 Argument

Premises

Rules of inference

3 Dialogue

“Justification”

Dialogue stages

General inference pattern

premise1,premise2, . . . ,premisenrule of inference−−−−−−−−→ conclusion,

We claim the conclusion to be true on the bases of our inference.

Claims can be contradictory on 4 different levels:

1 level of fact,

2 level of definition,

3 level of value,

4 level of policy.

1 level of fact,

3 level of value,

4 level of policy.

1 level of fact,

3 level of value,

4 level of policy.

1 level of fact,

3 level of value,

4 level of policy.

Premises

Definition (Premise)

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 practically don’t exist.

Premises

dynamic);

Premises

dynamic);

Premises

dynamic);

Premises

dynamic);

Premises

dynamic);

Rules of inferenceBack to question: How do we justify our convictions?

Definition (Argumentation scheme)

Argumentation schemes are forms of argument that capture stereo-

typical patterns of human reasoning, especially defeasible ones like

argument from expert opinion, that have proved troublesome to view

deductively or inductively.a

aD. Walton. Justification of argumentation schemes. 2005.

Argumentation schemesClassification(s)

Argument from generalization,

Argument form causal relation,

Argument form expert opinion,

Argument from sign,

Argument from analogy,

. . . . . . ..

. . . .

Argumentation schemes

Example

Premises:

(a) John is not looking me in the eyes when he talks about smth.

(b) Generally, avoiding eye contact is a sign of insincerity.

Conclusion: John is lying.

Argumentation schemesCritical questions

Argument from sign

Premises:

(a) A is true in this situation.

(b) Event B is generally indicated as true when its sign, A, is true in this kind of

situation.

Conclusion: B is true in this situation.

Critical questionsa

1 What is the strength of the correlation between A and B?

2 Do we (currently) know of any events other than B that would more

reliably account for A?

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

Argument from sign

Premises:

situation.

Critical questionsa

Argument from sign

Premises:

situation.

Critical questionsa

“Justification”Fundamental conceptsDialogue stages

Agenda

2 Argument

Premises

Rules of inference

3 Dialogue

“Justification”

Dialogue stages

Problem

People face conficts of:

opinions (what is morally right/what to do/what is the state of

matters/. . . ),

interests.

All we have are uncertain and context dependant arguments.

Question

How do we resolve those conflicts?

Problem

matters/. . . ),

interests.

Question

Problem

matters/. . . ),

interests.

Question

Solution

Answer

By testing our claims through process of questions and answers.

Definition (Dialogue)

Dialogue is a multilateral process of reaching a goal (often to resolve a conflict)

through exchange of locutions.

Examples of dialogues:

everyday discourse,

teacher–student dialogue,

court trials,

Plato’s dialogues.

Solution

Answer

everyday discourse,

court trials,

Solution

Answer

everyday discourse,

court trials,

Presumption/burden of proof,

burden of rejoinder,

commitments.

Dialogue stages

1 Opening stage (specification of the type and rules of the dialogue):

locution rules,dialogue rules,commitment rules,win-loss rules;

2 confrontation stage (pinpointing the conflict);

3 argumentation stage (the main part...);

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

Dialogue stages

Agenda

2 Argument

Premises

Rules of inference

3 Dialogue

“Justification”

Dialogue stages

FallaciesBack to question: What makes a good/bad justification?

Argument ad hominem (personal attack),

Argument ad baculum (resorting to force),

Argument ad verecundiam (bad usage of an argument from expert’s

opinion),

. . . .

Generally, you can find situations in which the above are not fallacious

arguments.

Some developments – argumentationSome developments – dialogue

Agenda

2 Argument

Premises

Rules of inference

3 Dialogue

“Justification”

Dialogue stages

1 Creating formal models helps us to understand the thing that we try to

formalise.

2 Formal models can be implemented.

1 Creating formal models helps us to understand the thing that we try to

formalise.

2 Formal models can be implemented.

Dung’s Argumentation Framework

P. M. Dung. On the acceptability of arguments. . . . 1995.

Carneades Argumentation Framework

T. Gordon, D. Walton. The Carneades Argumentation Framework. 2006.

Prakken’s Framework

H. Prakken. Coherence and Flexibility in Dialogue Games for Argumentation.

Agenda

2 Argument

Premises

Rules of inference

3 Dialogue

“Justification”

Dialogue stages

Conclusions

Informal logic aims at describing the human way of reasoning:

arguments are defeasible inferences of the form

premisesarg.scheme−−−−−→ claim,

where not only the premises, but also the application of argumentation

scheme must be justifiable.

dialogue is a method for evaluation of claims and arguments that support

There are promising (yet early) attempts of formal applications of informal logic.

Conclusions

Informal logic aims at describing the human way of reasoning:

arguments are defeasible inferences of the form

premisesarg.scheme−−−−−→ claim,

where not only the premises, but also the application of argumentation

scheme must be justifiable.

dialogue is a method for evaluation of claims and arguments that support

There are promising (yet early) attempts of formal applications of informal logic.

Thank you

. . . for your attention.

Informal logic - Warsaw University of...

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