Philosophy Now - Critical Reasoning by Marianne Talbot

Question 1

Introduction

As with any of our natural capacities, attempts have been made to develop a theory of reasoning. This theory is called logical theory. Logical theory is normative, meaning it sets standards, tells us whether we are reasoning well or badly.

Analysing Arguments

In analysing an argument we get rid of everything extraneous to the argument, thereby revealing its logical structure.

Evaluating Arguments

An argument’s being good or bad no more depends on the truth or falsehood of the premises than it does on the truth or falsehood of the conclusion. There are good arguments with false premises. And there are bad arguments with true premises.

For an argument to be good, the only thing that matters is whether its conclusion follows from its premises. The actual truth-values of its premises and conclusion are irrelevant. A good argument is such that if its premises are true, its conclusion must be true.

Soundness

We want our arguments to be good, such that their conclusion follows from their premises; but we also want them to be sound, meaning that their premises are true, and their conclusions follows from their premises.

Answer 1

We cannot logically require soundness of an argument. We often don’t know, after all, whether our premises are true or false.

The distinction between the argument’s being good and its being sound tells us how to go about questioning the conclusion of a good argument.

Deduction vs Induction

Deductive arguments when good are valid: if the premises are true the conclusions logically must be true. If an argument is deductively valid, and its premises are true, then it is logically impossible for the conclusion to be false. But I might have chosen to illustrate my case with inductive arguments.

Here is a good inductive argument:

Premise one: The sun has risen every day historically
Conclusion: The sun will rise tomorrow

You will note immediately that whilst it would be hard to say the conclusion of this argument doesn’t follow from its premises, the argument is not valid. Its premise might be true yet its conclusion false.

No inductive argument is valid. For inductive arguments, the conclusion following from the premises is a matter of a strong probability that it is true, given the truth of the premises. Every inductive argument tacitly relies on what Scottish philosopher David Hume called ‘The Principle of the Uniformity of Nature’ (PUN): the belief that the future will be like the past.

Question 2

We don’t, therefore, talk of inductive validity, but of inductive strength. Inductive arguments can be weak or they can be strong, or they can be anything in between. Induction doesn’t give us certainty, nor does it give us conclusivity.

Conclusivity means that if a deductive argument is valid, then it will remain valid whatever else we might learn.

Induction is Ineliminable

Induction might not give us certainty, conclusivity or systematicity. It might also be such that we can evaluate an inductive argument only in the light of our background knowledge of the world. But we cannot do without it.

That this is the case became clear when the philosopher of science Karl Popper tried to argue that science can do without induction. Popper argued that we never inductively confirm a theory, and must instead be content with falsifying it.

Answer 2

The only thing we can justifiable claim to know, he argued, is that a theory is false, never that it is true. However, in claiming this, Popper was tacitly relying on induction: after all, what makes us think that a theory that has been falsified on one occasion will be falsified on the next occasion, if it isn’t the inductive belief that the future will be like the past?

Induction is as important as deduction, but it is different. Understanding that and how it is different is an important part of sharpening your reasoning skills.

Conclusion

Reasoning is central to our notion of what it is to be human, but we can reason well or we can reason badly. Logical theory aims to identify what it is to reason well. By learning some logical theory, as you just have, you can improve your reasoning.