Logic 101 · Philosophy · Series

Logic 101: The Qualities of Good Arguments

In my last post I summarized twelve principles from Attacking Faulty Reasoning that constitute what T. Edward Damer calls “A Code of Intellectual Conduct.” (From here on in the post I will refer to this as simply the “Code.”) These principles are not only useful in the ways that I described in the last post (as both procedural and ethical standards). As we will see, they are also useful as a way to determine whether or not any arguments we reconstruct or raise are free from error.

According to Damer, an argument is a good one if it does not violate principles (6) through (10) of the Code.[1] Here are those principles one more time:

6. The Structural Principle: Adhere to the rules of argumentation that produce valid, sound deductive arguments and strong inductive arguments.

7. The Relevance Principle: Don’t bring up arguments or counter-arguments that are tangential to what’s being discussed.

8. The Acceptability Principle: All things being equal, provide premises for your arguments that any rational, mature person could accept.

9. The Sufficiency Principle: When proving premises in an argument, make sure that those premises actually prove what you claim they do.

10. The Rebuttal Principle: When an opponent raises objections that pose a serious threat to our arguments, those objections should receive an answer.

If an argument follows all of these principles, it is a fallacy-free argument. Only fallacy-free arguments are good arguments. But even good arguments aren’t always convincing. It is necessary for a good argument to be fallacy-free in order to be convincing, but it is not sufficient. (I’ll explain this distinction in a later post.)

For now I’ll expand on what fallacy-free arguments are.

Two Types of Validity

What Damer means by “The Structural Principle” is that arguments should be put together (“structured”) using the established conventions that make them good ones, regardless of which type of argument is being made. So there are actually two principles that go into this one:

6a. The Deductive Principle: Arguments that are intended to be deductive should be structured in such a way that the conclusion cannot be false while the premises are true. I stated in my previous discussion about deductive arguments that they should be formally valid. Formal validity is the first type of validity.

6b. The Inductive Principle: Arguments that are intended to be inductive should be structured in such a way that the conclusion is probably true if the premises are true. Inductive arguments must have inductive strength.

When an argument violates The Structural Principle, this can mean either (1) that the argument is formally invalid (if the argument is supposed to be deductive) or (2) that the argument is inductively weak.

But these are only two ways that The Structural Principle can be violated. Both deductive and inductive arguments are bad ones if they are informally invalid. To be informally invalid is to argue in such a way that, regardless of the form or structure of the argument, the conclusion cannot be justified. Informal validity is the second type of validity. If any argument violates principles (6) through (10) of the Code, that argument is informally invalid.

To summarize, good arguments must be informally valid by following principles (6) through (10) above. Deductive arguments should be formally valid as well.

More on The Acceptability Principle

Good argument must also meet two other requirements: they must use precise language and they must have true premises. Both of these requirements are a part of The Acceptability Principle.

Let’s start with clear language. Unless a premise is first understood, it cannot be accepted. To be accepted, an argument must use terms that are clear and unambiguous.

When a term is used across multiple premises, that word must be used with the same meaning in those premises. The technical way to say this is that your terms should be univocal. When the same word is used in two different ways in an argument, that term is equivocal. Equivocal terms are ambiguous, since we don’t know precisely which meaning is referred to by those terms.  Ambiguous terms are unclear, by definition.

But we can fail to use clear language when we don’t explain what we mean by our terms in a way that others can readily understand. If a term isn’t explained well, then we cannot tell if it is ambiguous. So, in order for an argument’s premises to be acceptable, it must use terms that are unambiguous and clearly explained.

But using imprecise language is only one way to violate The Acceptability Principle. A premise is acceptable if it is more plausible than its negation. Here’s what I mean. Suppose there’s a premise that says this:

(P1) The universe is 6,000 years old.

The negation, or opposite of (P1) would be:

(P1*) The universe is not 6,000 years old.

For (P1) to be acceptable to us, there must be better reasons for accepting it than its opposite (P1*). That’s what it means for (P1) to be more plausible than its negation.

If a premise is more plausible than not, then we have good reason to think that it is true. By “true” I do not mean “true with certainty.” There are very few premises that we can utilize in everyday arguments that are true with certainty, so it doesn’t seem right to make certainty a condition of a good argument.

This might be confusing, but even in a deductive argument the conclusion isn’t known with certain. The conclusion of a deductive argument must be true if the premises are true, but that doesn’t mean that the conclusion must be certain.


For a premise to be plausible it must be acceptable to a mature, rational person under the right circumstances and in the right context. Here’s a summary of some of the ways Damer says we can tell a premise is plausible:[2]

  1. It is common knowledge.
  2. It is confirmed by personal experience or observation.
  3. It is supported by viable eyewitness testimony.
  4. It is supported by a qualified, relevant authority.
  5. It is the conclusion of another good argument.
  6. It is not based on an implausible assumption and does not lead to any implausible assumptions.

There are many other factors that make premises seem correct to us. Sometimes the truth of a premise comes down to intuition, or what strikes us initially as being true, as well. No matter what, it is important to consider how we are justified in accepting or rejecting a conclusion.


Logic textbooks and courses make a big deal out of what makes arguments good ones. They all agree that an argument must:

  1. Be deductively valid or inductively strong.
  2. Be informally valid.
  3. Use precise language.
  4. Have true premises (in the sense of being more plausible than not).

Using T. Edward Damer’s book Attacking Faulty Reasoning as our guide, we’ve seen that this means that a good argument does not violate principles (6) through (10) of the Code of Intellectual Conduct.

Since arguments are always raised in settings that involve interaction, the next post will build on the last two and discuss how to have fruitful conversations.



[1] T. Edward Damer, Attacking Faulty Reasoning, 6th ed. (Belmont, CA: Wadsworth Cengage Learning, 2009), 30.

[2] Ibid., 34-36.

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