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 1Premise 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 n Therefore (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 tax will 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 tax will increase consumption

Using causal generalisations in arguments Income tax is lowered Consumption will increase The same happened in Germany Lowering income tax will increase consumption

‘forward’ use of causal generalisations Income tax is lowered Consumption will increase Lowering income tax will increase consumption

‘backward’ use of causal generalisations Consumption has increased Income tax was lowered Lowering income tax will 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 V Therefore (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 actions A1 has the highest expected utility of A1, …, An Therefore, 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?