There is no uncontroversial “one size fits all” definition for good arguments that will tell us whether an argument is a good argument or not. The term is a bit vague and there is room for disagreement. We can’t give a list of necessary and sufficient conditions for when an argument is a good one that all philosophers will agree with. Even so, what constitutes good arguments involves rational criteria. In fact, arguments are good insofar as they are “rationally persuasive.” Consider the following six ways we can describe good arguments:
- We can give uncontroversial examples of good arguments.
- Good arguments must not be fallacious.
- Good arguments are rationally persuasive.
- The premises of good arguments are sufficiently justified.
- The conclusion of good arguments are likely true given the assumption that the premises are true.
1. We can give uncontroversial examples of good arguments.
Here are two uncontroversial examples of a good arguments:
- All dogs that have been studied by scientists were discovered to be mammals.
- Therefore, all dogs are probably mammals.
This is an inductive argument. Inductive arguments generalize using limited information to attempt to provide us with a conclusion that is likely true given the premises. Inductive reasoning is used when we try to make plausible predictions or use statistics.
- All dogs are mammals.
- If all dogs are mammals, then all dogs are animals.
- Therefore, all dogs are animals.
This is a deductive argument. Deductive arguments are meant to prove that a conclusion must be true as long as we assume the premises are true.
2. Good arguments must not be fallacious.
Fallacies are errors in reasoning. Good arguments must not be fallacious because such argument don’t give us a good reason to believe something. Consider the following three types of fallacies:
- Straw man argument – To mischaracterize an argument or belief in order to make it seem less reasonable than it really is. For example, imagine that Samantha argues that “we should continue to use the death penalty because some people will decide not to commit murder knowing they could be executed.” I would then give a straw man argument if I responded by saying, “Samantha thinks that we should continue to use the death penalty because no one will choose to commit murder knowing they could be executed for it, but obviously murderers are willing to take that chance in places that still use the death penalty. They are not deterred knowing about the harsh punishment.” In this case I attempted to refute an argument, but it is a notably worse argument than the one given by Samantha. She never claimed that the death penalty would deter everyone from committing murder, but only that it could deter some people from committing murder.
- False dilemma – Also known as “black and white thinking.” An argument that requires us to only consider so many options when there is at least one reasonable option that’s ignored. For example, a person might argue that “the President of the United States is either a dog or a cat. He’s not a dog, so he’s a cat.” There is at least one other option—the President is a human being.
- One-sidedness – Also known as “suppressed evidence.” An argument commits the one-sidedness fallacy when it gives considerations in favor of a conclusion but it leaves out important considerations against the conclusion. For example, a person might argue that we should vote for the Democratic candidate for president because the Republican candidate supported the bank bailout when both candidates actually supported the bailout.
3. Good arguments are rationally persuasive.
Good arguments give us a sufficient reason to believe something is true insofar as the reason is compatible with rationality. What exactly is “rationality?” At the very least rationality requires that we don’t contradict ourselves or use fallacies. However, rationality in a broad sense involves what we should believe:
- Rationally required – These are propositions that we should believe, and it would be wrong not to believe them. We would be irrational not to believe these things. For example, we are rationally required to believe that at least three people exist based on our experiences of our family, friends, and strangers. A belief is only rationally required if we have a very strong reason to believe it’s true.
- Rationally permissible – These are beliefs that are optional. We need not believe them, but there’s nothing wrong with believing them. For example, it seems perfectly reasonable to believe that computers will be greatly improved within the next ten years considering how much they have been improved over time in the past. A belief is only rationally permissible if we have a good enough reason to believe it’s true.
- Rationally impermissible – These are propositions that we should not believe—it would be wrong to believe them. We could say it would be irrational to have these beliefs. For example, it is rationally impermissible to believe that we can jump to the moon based on our experiences of our human limitations and the laws of nature. A belief is rationally impermissible only if we have a very good reason to think it’s false.
How do we know exactly if a belief is rationally required or permissible? That is a controversial issue in epistemology (the philosophical study of knowledge, rationality, and justification). However, this issue is particularly related to the concept of “justified beliefs,” which is discussed below.
4. The premises of good arguments are sufficiently justified.
What exactly does it mean for a premise to be sufficiently justified? It means that it’s rational to believe the premise is true because we have a good enough reason to believe it—there is enough evidence to warrant the belief. Some beliefs have such a strong justification that we have to believe them, some beliefs are justified enough to be compatible with rationality, and we have such strong justification against certain beliefs that the beliefs are incompatible with rationality.
Keep in mind that the classic definition of “knowledge” is of a “justified true belief.” If no beliefs are justified, then it would be impossible to know anything. Yet we know lots of things. We know “1+1=2,” we know that more than three people exist, and we know that dogs are mammals.
If we have a good argument that leads to a belief in a true conclusion, then it is reasonable to say that we “know the conclusion is true.” Even so, what qualifies as a “sufficient justification” is not always easy to understand. A permissive view is that a person who has rationally permissible premises only needs premises that are not yet refuted similar to a scientific hypothesis that is assumed to be true until proven otherwise.
Additionally, it is not always obvious what kind of a justification makes our beliefs likely true or rationally required. For example, some philosophers argue that the only justifications that matter involving the world are those involving observation, but other philosophers believe that intuition (a form of justification that is more difficult to understand) should count for something as well. Intuitive beliefs are those that we think seem true when we have a hard time explaining how we can know they are true. For example, it can be argued that we find it intuitive that “2+2=4” and yet we have a hard time explaining how we can know it to be true. It would also be “counterintuitive” to find out that “2+2=5.”
Another example of an intuitive belief is that at least one of two contradictory statements are always false. Two statements are contradictory when one statement is incompatible with the other. For example, “Socrates is a man” contradicts “Socrates is not a man.” It would be counterintuitive to find out that Socrates is both a man and not a man.
5. The conclusion of good arguments are likely true given the assumption that the premises are true.
Premises of good arguments need to be good reasons to believe that the conclusions are true, which means that if the premises of a good argument are true, then the conclusion is likely true as a result. It is unlikely for the premises of a good argument to be true and the conclusion to be false at the same time. In other words, good deductive arguments are logically valid, and good inductive arguments are logically strong.
Logically valid arguments can’t possibly have true premises and a false conclusion at the same time because they have a logically valid argument form. For example, “A. If A, then B. Therefore, B” has a logically valid argument form. An argument with this form is “All pit bulls are dogs. All dogs are reptiles. Therefore, all pit bulls are reptiles” is a valid argument because it’s impossible for the premises to be true and the conclusion to be false at the same time. Even so, one of the premises is false, and the conclusion is false.
Logically valid arguments with true premises always have true conclusions. These arguments are logically sound. For example, “All dogs are mammals. If all dogs are mammals, then all dogs are animals. Therefore, all dogs are animals.” The premises and conclusions of logically sound arguments are always true.
Logically strong inductive arguments are unlikely to have true premises and a false conclusion at the same time. If we assume the premises are true, then the conclusion is also likely true. For example, “All dogs we have ever seen were reptiles. Therefore, all dogs are probably reptiles.” This is an inductively strong argument, but the premise is false.
An argument is logically cogent if and only if it’s logically strong arguments and has true premises. For example, “All dogs we have ever seen were mammals. Therefore, all dogs are probably mammals.”
All good deductive arguments are valid and all good inductive arguments are strong, but not all good arguments have true premises because we don’t need to know that the premises are true. Instead, the premises merely need to be sufficiently justified. For example, consider Argument 2 from above:
- All dogs are mammals.
- If all dogs are mammals, then all dogs are animals.
- Therefore, all dogs are mammals.
Both premises are confirmed by our best science, but it is possible that the first premise false. We don’t know it’s true for absolute certain. Perhaps one day we will find out that dogs are a species that merely greatly resembles mammals. Even so, this is still a perfectly good argument. It is perfectly reasonable to use the results of our best science as premises for our arguments, even though the conclusions of our best science is occasionally discovered to be false.
Understanding good argumentation requires us to better understand rationality and justification. Although philosophers do not agree unanimously about what makes a good argument, there is a great deal of agreement. There are uncontroversial examples of good arguments, there are uncontroversial examples of fallacies, good arguments are meant to help us understand what is true, and good arguments are meant to help us understand what we should believe. Finally, good arguments are central to our understanding of knowledge—to know anything implies that we had a sufficiently good reason to believe it. If we have a good argument for a conclusion and the conclusion is true, then we know the conclusion is true.
Update (12/3/2012): Various corrections and clarifications were made.