Legal Argumentation 3

Henry Prakken

April 4, 2013

The structure of arguments:basic elements

(Basic) arguments have: Premises (grounds) A conclusion A reasoning step from the premises to

the conclusion

Conclusion

Premise 1 Premise n…..

therefore

Three types of counterarguments

(Basic) arguments have: Premises (grounds) A conclusion A reasoning step from the premises to the

conclusion So arguments can be attacked on:

Their premises Their conclusion

Except if deductive The reasoning step from premises to

conclusion Except if deductive

Argument schemes: general form

But also critical questions Negative answers are counterarguments

Premise 1, … , Premise nTherefore (presumably), conclusion

Overview of course Week 1:

Basic structure of arguments Combinations of premises implicit premises Multi-step arguments

Week 2: Arguments and counterarguments Argument schemes (1)

Week 3: Argument schemes (2) Evaluating arguments

Causal relations Lowering income tax will increase

consumption Not an argument:

Income tax is lowered

Consumption will increase

Causal relations Lowering income tax will increase

consumption But a statement:

Lowering income taxwill increase consumption

Using causal generalisations in

arguments

Income tax is lowered

Consumption will increase

Using causal generalisations in

arguments

Income tax is lowered

Consumption will increase

Lowering income taxwill increase consumption

Using causal generalisations in

arguments

Income tax is lowered

Consumption will increase

The same happened in Germany

Lowering income taxwill increase consumption

‘forward’ use of causal generalisations

Income tax is lowered

Consumption will increase

Lowering income taxwill increase consumption

‘backward’ use of causal generalisations

Consumption has increased

Income tax was lowered

Lowering income taxwill increase consumption

Causal explanation (Abduction)

Critical questions: Could Q be caused by something else? Does P cause something of which we know

it is not the case?

P causes Q Q has been observed so (presumably), P

Arguments from consequences

Critical questions: Does A also have bad (good) consequences? Are there other ways to bring about G? ...

Action A brings about G, G is good (bad)Therefore (presumably), A should (not) be done

Example (arguments pro and con an action)

We should make spam a criminal

offence

Making spam a criminal offence reduces spam

Reduction of spam is good

We should not make spam a

criminal offence

Making spam a criminal offence

increases workload of police and

judiciary

Increased workload of police and

judiciary is bad

Example (arguments pro alternative actions)

We should make spam a criminal

offence

Making spam a criminal offence reduces spam

Reduction of spam is good

We should make spam civilly

unlawful

Making spam civilly unlawful reduces spam

Reduction of spam is good

Arguments from consequences (generalised to causal chains)

Critical questions: Does A also have bad (good) consequences? Are there other ways to bring about G? ...

Action A brings about G1, which brings about ….… which brings about Gn Gn is good (bad)Therefore (presumably), A should (not) be done

Causal chains Toppling the Hussein regime will pave the

way for democracy in Iraq Democracy in Iraq will advance the cause

of democracy elsewhere in the Middle East Advancing the cause of democracy will

diminish the risk of anti-American violence Diminishing the risk of anti-American

violence is good Therefore, we should topple the Hussein

regime

Refinement: promoting or demoting legal

values

Critical questions: Are there other ways to cause G? Does A also cause something else that

promotes or demotes other values? ...

Action A causes G, G promotes (demotes) legal value VTherefore (presumably), A should (not) be done

Example (arguments pro and con an action)

We should save DNA of all citizens

Saving DNA of all citizens leads to

solving more crimes

Solving more crimes promotes

security

We should not save DNA of all

citizens

Saving DNA of all citizens makes

more private data publicly accessible

Making more private data

publicly available

demotes privacy

Example (arguments pro alternative actions)

We should save DNA of all citizens

Saving DNA of all citizens leads to

solving more crimes

Solving more crimes promotes

security

We should have more police

Having more police leads to solving more

crimes

Solving more crimes promotes

security

Comparing action proposals For every proposal that is based on

acceptable premises: List all legal values that it promotes or demotes

Determine the extent to which the proposal promotes or demotes the value

Determine the likelihood that such promotion or deomotion will occur

Determine the relative importance of the values at stake

Then weigh the pros and cons of all proposals But how?

Expected-utility arguments The expected utility of an action is (roughly)

the degree of goodness of badness (= utility) of the action’s consequences multiplied with the likelihood that these consequences will occur

A1,.., An are all my possible actionsA1 has the highest expected utility of A1, …, AnTherefore, A should be done

Classification of arguments

Conventional classification: arguments are deductive, inductive or abductive

However: Only applies to epistemic arguments “inductive” is ambiguous There are other types of arguments

Better classification: arguments are deductive or presumptive (defeasible)

Evaluating arguments Does it instantiate an acceptable

argument scheme? Have all its counterarguments been

refuted? Are its premises acceptable? If presumptive: what about attacks on

inference or conclusion? Argument schemes help in identifying sources

of doubt in an argument. Has the search for counterarguments

been thorough enough?

Can be indirect

Fallacies There are conventional lists of fallacies

Affirming the consequent, authority, attacking the source, ...

But such arguments often make sense! They are schemes for presumptive

arguments What is important is: can they be

defended against attack?