CJ Blunt

WritePhilosophy

Criticising an argument: Reductio & Dilemmas

3 minute read

It is crucial to understand the approaches to criticising philosophical positions which philosophers employ—both to use these tools to criticise others’ work, and to anticipate criticisms of your own work. Here, we’ll explore two common approaches to criticising philosophical positions: reductio ad absurdum and dilemmas. A third approach, providing counterexamples, has its own page: see the guide to counterexamples. For advice on criticising philosophical arguments see the page on argumentative fallacies.

Reductio ad Absurdum

Reductio ad absurdum translates to ‘reduction to absurdity’. It is a powerful philosophical tool, used to show that a position must be false, because absurd consequences would follow if it were true. It uses the logical form modus tollens:

P -> Q

Not Q

Therefore, Not P

This is a logically valid argument.

When constructing a reductio argument, the crucial step is deducing a consequence of the position which is sufficiently absurd as to be unacceptable. The best reductio arguments will deduce a contradiction from the thesis. However, reductio ad absurdum arguments can also be constructed by deducing a simply unpalatable consequence from the thesis. For instance:

If determinism is true, then no actions are morally right or wrong.

Actions are morally right and wrong

Therefore, Determinism is false.

Responding to Reductio arguments

There are two ways to respond to a reductio:

  1. Bite the bullet. ‘Biting the bullet’ means accepting the unpalatable consequence. For instance, in the determinism example, a determinist could simply accept that there is no morality.
  2. Refute the argument—show that the absurd consequence does not actually follow from the position. In the example above, this would mean showing that actions can actually be moral or immoral despite determinism.

Dilemmas

Dilemmas are complex forms of reductio argument, where there are two (and only two) possible options for a defendant of a position, and both lead to unpalatable consequences. Note that this differs from the colloquial sense of ‘dilemma’ that you might encounter in, say, ethics—an ethical dilemma is a situation in which it is difficult to decide which course of action is the right one. Argumentative dilemmas are distinct from these tricky problems.

A dilemma has the logical form:

P -> (Q or R)

Q -> S and R -> T

(Not S) and (Not T)

Therefore, Not P

Again, this is a valid inference.

For instance, consider the following argument:

If determinism is true then either we are not morally responsible for our actions or we are morally responsible for actions we could not have avoided doing. (P -> (Q or R))

If we are not morally responsible for our actions then all punishment and reward is unfounded, and if we are morally responsible for actions we could not have avoided doing then morality is just a matter of luck. ((Q -> S) and (R -> T))

It is not the case that all punishment and reward is unfounded, and it is not the case that morality is just a matter of luck (Not S and Not T)

Therefore, determinism is false. (Not P)

In a dilemma, we call the P -> (Q or R) premise the disjunctive premise (as it contains an ‘or’ phrase) and the (Q -> S and R -> T) premise the conjunctive premise (as it contains an ‘and’ phrase).

In order for a dilemma to be sound, it must be the case that

  1. The absurd consequences (S and T) do follow from the two options (Q and R)
  2. The two options (Q and R) are the only options available for a defender of P.

How to respond to a dilemma

There are three ways out of a dilemma:

  1. Bite the bullet. As with a reductio argument, if the absurd consequences are not contradictions, you have the option to bite the bullet and accept one of the absurd consequences, perhaps arguing that it is not as absurd as it might seem. For instance, a defender of determinism might accept that morality is a matter of luck.
  2. Go between the horns. The two options in a dilemma are called the “horns of the dilemma”. Going between the horns means showing that there are in fact other options available—in other words, showing that the disjunctive premise is false. If you successfully go between the horns, you have shown that the argument was a false dichotomy.
  3. Grasp a horn. Grasping one of the horns of the dilemma means showing that one of the absurd consequences which is supposed to follow from a horn of the dilemma does not in fact follow. So, for instance, the proponent of determinism could grasp the first horn of my dilemma by showing that despite no one being morally responsible for their acts, punishment and reward systems are morally justified.

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