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The Amateur Logician Tutorial:
An Invitation | Arguments | Evaluating Arguments | Laws of Thought | Ontology & Logic | Concepts, Signs, & Names | Categorical Propositions | Negations & Complements | Distribution | Euler’s Circles & Venn Diagrams | Predicables | Categories | Definitions | Square of Opposition | Equivalent “Immediate Inference” | Traditional “Immediate Inference” | Informal “Immediate Inference” | Categorical Syllogism | Syllogisms & Venn Diagrams | Moods & Figures of Syllogisms | Polysyllogisms & the Sorites | Enthymemes | Compound Propositions | Conditional Propositions & Conditional Syllogisms | Conditional Contrapositions, Reductions, & Biconditionals | Conjunctions, Disjunctions, & Disjunctive Syllogisms | Dilemmas | Modal Propositions | Reductio ad Absurdum Arguments | Deduction & Induction | Inductive Abstraction | Inductive Syllogisms | Mill’s Inductive Methods | Science & Hypothesis | Formal Fallacies | Testimony & Unsound Authority | Informal Fallacies & Language | Diversion & Relevancy Fallacies | Presumption Fallacies | Causal & Inductive Fallacies
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An Introduction to Evaluating Arguments
When evaluating arguments, always identify an argument’s premises and its conclusion.
First, make sure there actually is an argument!
Second, find the conclusion.
Third, find its premises.
Fourth, attempt to determine the truth or otherwise of those premises..
Fifth, attempt to determine if those premises justify the conclusion.
Is an argument being made?
A bare assertion is not an argument. Someone emoting their feelings is not an argument. Questions and suggestions aren’t arguments.
An argument will always contain a conclusion that declares something to be the case. It can be true or false. And an argument will have premises that attempt to justify that conclusion with evidence.
Indicator words can help us spot an argument’s conclusion and its premises.
Often the conclusion can be identified with words like “therefore,” “hence,” “it follows,” “as a result,” “it can be inferred that,” “consequently,” “so,” “ergo,” etc.
Premises can be identified with words like “as shown by,” “for reason that,” “given that,” “because,” “due to,” “owing to,” “insomuch as,” “as result of,” etc.
Useful Tip: if these indicator words aren’t used, insert them yourself. This will help you re-construct and evaluate the (possible) argument.
Are the premises true? A question of well-groundedness.
We need to judge the truth (or falsity) of the premises.
An argument with true premises is said to be “well-grounded.”
However, it’s not enough that the premises be true.
Terms used in the premises need to be unambiguous, clear, and used consistently.
A premise with a meaningless term makes the premise meaningless.
And if, for example, two premises use the same term in totally different ways, then we cannot legitimately relate the premises together to make an inference.
Pretend I argue: “All heavy things weigh over ten pounds. This book by Kant is heavy. Thus, this book weighs over ten pounds.” What went wrong?
Does the conclusion follow from the premises? A question of validity.
We need to determine if the argument obeyed the rules of logic.
What’s called “formal logic” is a limited — albeit still powerful — tool. It doesn’t strictly deal with the particular content of premises. It alone cannot tell us if a premise is true or false. It takes premises for granted.
Formal logic, instead, deals with validity. An argument is valid if and only if it obeys the rules of logic. That’s it! Thus, in a valid argument, the conclusion can be legitimately derived from the given premises (but those given premises might be false).
An argument that is valid and well-grounded is said to be “sound.”
Insofar as we have true premises and a valid argument, the conclusion cannot be false. It’s guaranteed to be true, i.e., the conclusion has been proven.
Please remember, a valid argument may have a false conclusion because at least one premise is false. Thus, just because the argument is valid, doesn’t mean the conclusion is true. That’s why we need to determine if the argument is valid and if it has true premises.
Consider the possibilities. True premises and an invalid argument may or may not have a true conclusion. That conclusion may be true or may be false. Similarly, false premises and a valid argument may or may not have a true conclusion. False premises and an invalid argument may or may not have a true conclusion.
However, if we know for a fact that the conclusion is false and the argument is valid, then we know for a fact that at least one premise must be false. Additionally, if we know for a fact that the conclusion is false and the premises are all true, then we know for a fact that the argument must be invalid.
A Sound Deductive Argument:
All True Premises (with clear and consistently used terms) + Valid Inferences
= A True Conclusion
Assessing and constructing arguments is a skill. It takes practice.
Don’t worry if things appear a little hazy at the moment. What exactly is a valid argument? What is a good rule of inference? What exactly does “inference” mean? These are questions to answer in our study of logic.
Nevertheless, we all have some intuition about what makes a valid argument. Logic helps us enhance this intuition. It turns argumentation into a philosophical science. It’s not only a remarkable tool — and a remarkable science — it’s truly an exciting field of study.
