Lesson 2.04: Weaknesses in Reasoning

Inadequate support

It is a weakness if reasoning supports only part of the conclusion which is drawn from it, or if a moderate claim or intermediate conclusion is used to support a conclusion which would follow only from a stronger version.

Inconsistency

It is a weakness if one part of an argument's reasoning contradicts, or is inconsistent with, another part. 

This is the first paragraph of an argument about change. The final paragraph ofthat argument, including the main conclusion, is:

Admittedly, some changes do ultimately turn out to have been for the better, but the problem is that we cannot tell beforehand which ones they will be. It is always more likely that any particular proposal will lead to catastrophe than that it will result in an improvement. So the best practice is to be safe, by resisting all change. This reasoning is weakened by two inconsistencies.

This reasoning is weakened by two inconsistencies.

1. The word 'improvement' is used in different senses in the two paragraphs. The point being made in the first paragraph, that changes which are called 'improvements' often (or 'always') do not make things better, is weakened by the use of the word in its usual sense in the final paragraph. Since this inconsistency makes the overall argument less clear than if the word had been used consistently, it was probably unintentional.

2. The more serious weakness is that the first sentence claims that all changes are for the worse, while the final paragraph admits that some changes are for the better. The support which the first paragraph gives to the conclusion is weakened by this concession.

Analogies

Arguments often make use of analogies, in which an unfamiliar concept is illustrated by reference to something more familiar. Politicians frequently use analogies, for example, 'Managing the budget of a country is just like managing the budget of a household: you can't spend more than you earn.' It is not a valid criticism of an analogy to say that the two entities are different, because that is the whole nature of an analogy. Even imperfect analogies can strengthen an argument, but a wild analogy which lacks significant points of similarity or has crucial differences constitutes a weakness in reasoning.

An example of a weak or false analogy is that tobacco is like arsenic, because both of them kill people, and therefore the sale of tobacco should be controlled by the Poisons Act. The weakness of this analogy is that the differences between arsenic and tobacco are crucial to the issue. No one consumes arsenic for pleasure; the harm done by smoking tobacco products is indirect, long term and a matter of risk rather than certainty.

Reliance

The fact that you disagree with a claim or a conclusion does not constitute a weakness in reasoning. However, reliance on an unsupported claim or unstated assumption which many listeners or readers would be likely to reject does constitute a weakness, because it means that anyone who rejects the claim, definition or assumption can reasonably also reject the conclusion. So although identifying unstated assumptions is part of analysing arguments, it can also be a valid way of answering an evaluation question, if the assumption weakens the reasoning.

Responding to a counter

It is not a weakness for an argument to be one-sided. Someone defending one point of view is under no obligation to show balance.

But it can be a weakness if the proponent fails to foresee and respond to an obvious objection to a claim or line of reasoning, because this omission may cause most of the audience or readership to reject the argument.

The use of a counter assertion or counterargument with a response can be an effective technique in an argument, but giving the counter without responding to it weakens the argument, because it is doing the work of opponents for them.

Many flaws and weaknesses can be alternatively expressed in terms of assumptions, and that approach is just as acceptable as identifying the technical term.