Formal logic can help us achieve clarity and relevant arguments, but there are other requirements for a good argument. Most philosophers seem to get caught up discussing “fallacies” (errors in reasoning) rather than “good reasoning.” I will discuss the following four requirements for writing good arguments and the corresponding fallacies for failing to achieve the requirements:
- Supporting Evidence
- Relevant Evidence
- Consider all Viable Options
Arguments must have premises and a conclusion. Premises are statements that must be accepted before the conclusion is accepted. Premises could be considered “evidence” for the conclusion, but even premises must not be accepted without evidence. Sometimes we might accept a premise because it is “taken for granted” as true, but that tends not to be acceptable unless the premise has already been established as true.
An argument can only have relevant supporting evidence if (a) the conclusion is appropriately modest, (b) the premises are more certain than the conclusion, and (c) the conclusion isn’t illegitimately absurd.
The premises of an argument must lead us to the conclusion. If the argument is valid and the premises are true, then we have no choice but to accept the conclusion. Such a conclusion is appropriately “modest.” For example:
- If Socrates is a man, then he is mortal.
- He is a man.
- Therefore, he is mortal.
The conclusion must be accepted because the premises are certain (or close to being certain).
Overly ambitious conclusions: A conclusion that is not proven from the premises is an inappropriate sort of conclusion. Such conclusions tend to be “overly ambitious.” For example:
- If Socrates is a philosopher, then he is relatively wise.
- Socrates is a philosopher.
- Therefore, Socrates knows that the Earth is the third planet from the sun.
It is common knowledge that the Earth is the third planet from the sun and we would expect that relatively wise people would know such a thing, but that is only common knowledge in our day and age. Socrates was from a different period of time, so he might have not known. The conclusion is overly ambitious because we can only accept the conclusion given certain unstated assumptions.
An overly ambitious conclusion reveals that an argument is logically invalid. Even if the premises are true, the conclusion might not be true.
Less Certain Conclusions:
Conclusions should be less certain than the supporting evidence. Conclusions must not be more certain that the premises or the premises aren’t “evidence” for the conclusion. Imagine that someone argues the following:
- If people exist, then atoms exist.
- People exist.
- Therefore, atoms exist.
This argument is logically valid, but we are more certain that people exist than atoms exist. The fact that people exist can’t be taken to be evidence that atoms exist. That isn’t to say that atoms don’t exist. We just know less about atoms existing than people.
To have a conclusion that is more certain than the premises is a fallacy, but I don’t know the name of it. It is basically an “overly modest argument.” It might not have a name. I will call such a fallacy a “non-argument” because no real argument is given to accept the conclusion.
Also consider the following argument that I mentioned in my essay, “William Lane Craig’s Moral Argument For God“:
“If I am in a dream world, then I can sit on this chair. I am in a dream world. Therefore, I can sit on this chair.” We know I can sit on this chair, but we don’t know I am in a dream world. We find it very implausible that I am currently in a dream world, so such premises don’t seem to give “evidence” of the fact that I can sit on this chair.
Even worse than having a non-argument is having an illegitimately absurd conclusion. Absurd conclusions are extraordinary claims, and my point here is merely that extraordinary conclusions require extraordinary evidence. An absurd conclusion can be a conclusion that is almost certainly false even if the premises seem to be probably true. It is impossible to have an illegitimately absurd conclusion if the conclusion is appropriately modest, so the premises used must be questionable. But the fact that questionable premises can lead us to an absurd conclusion just makes us that much more certain that a premise has to be false. For example:
- I have existed for the past 29 years.
- The past resembles the future.
- Therefore, I will always exist.
Some people can’t imagine not being immortal and they believe they probably have an immortal soul. After all, we have existed all our lives. However, the conclusion is so incredible that one of the premises is almost certainly false. In this case the premise “the past resembles the future” seems to be taken the wrong way. If we are ever to accept the immortality of the soul, we will need a much better argument than this.
To have an absurd conclusion, such as the argument above, is to commit a fallacy, but I don’t know if it has a name. I will call it “ergo absurdum” (therefore absurdity).
Another example of an argument with an absurd conclusion is the following:
- Many people have “past life experiences” that provide insightful information.
- Either past life experiences are caused by past lives or dreams.
- It is very unlikely that a dream lead to such insightful information.
- Therefore, some people probably have past lives.
Although all of the premises look very likely to be true, the conclusion is absurd. The problem is that we have good reason to suspect that at least one premise is false. Perhaps there are other explanations for past life experiences than the two mentioned, and perhaps dreams can lead to the insightful information given by past life experiences. The fact is that we are uncertain about the premises all being true, and extraordinary conclusions require extraordinary evidence. Such extraordinary evidence isn’t given.
The evidence used in arguments must be relevant or we have no reason to trust them. The fact that bread has always been nutritious (rather than poison) makes it reasonable to think bread is still nutritious. However, people seem to be drawn to distractions (red herrings) rather than relevant reasons.
For example, the fact that the Soviet Union had universal health care doesn’t prove that universal health care is wrong. If everything the Soviets did was wrong, then we should never eat food or have sex. The temptation to dismiss some idea out of hand just because it was endorsed by an undesirable person or society is just a problem with human psychology.
The fallacy of using irrelevant evidence for a position is often called the “red herring” fallacy. Red herring fallacies are very common when people give “objections” to other arguments. Why? We often ignore the other person’s argument and just argue against their conclusion. We have a hard time giving relevant evidence against one conclusion and for another. For example, consider the following argument:
- Abortion kills people.
- Killing people is always wrong.
- Therefore, abortion is forbidden.
A common response is that abortion should not be forbidden because that would violate women’s rights. However, women’s rights are somewhat irrelevant to the above argument. If we accept the premises, then the conclusion follows. If women’s rights prove that abortion isn’t forbidden, then we are stuck with a contradiction: Abortion is forbidden and it isn’t.
A correct objection to the abortion argument is to challenge one of the premises. Is killing people always wrong? If so, war should be entirely illegal. Does abortion kill people? If fetuses are people, then perhaps dogs are as well.
If we find it very important to argue against someone’s conclusion, then we can do so, but we should first argue against one of the premises.
Consider all Viable Options
Arguments require that we accept that something is true instead of something else. Every single premise could be challenged if it doesn’t describe reality perfectly. When we argue that Einstein’s theory of relativity is true, we need to take a look at how much better it is than any alternative. The same goes for any other theory.
It is difficult for us to consider every viable option, so beliefs that fail to do so are common. Consider the following assertions:
- Either communism is good or universal health care is bad.
- Ether creationism is true or evolution is true.
- Either God exists or morality is just a matter of taste.
We might wonder, Why can’t both be false? Maybe capitalism is mostly good, but universal health care can also be good. There are often more options than we see at first. To assume less viable options than really exist is to suppress evidence and commit a popular fallacy known as the “false dilemma.”
When we object to an argument, we need to be able to describe it and fully understand it or what we have to say will be irrelevant. To do so is to be “charitable.” To misunderstand or misrepresent another people’s view could destroy our chances of saying anything relevant. Consider the following argument:
- People who believe in God life a better life.
- We have some reason to engage in actions that offer us benefits.
- Therefore, we have some reason to believe in God.
Someone might then disagree with you and say the following: “You are saying that everyone has to believe in God because it offers us benefits, but we shouldn’t have to believe something just because it benefits us in some ways!” This argument has misrepresented the argument because having some reason to believe in God is much different from the belief that “everyone must believe in God.” Such an argument is totally irrelevant.
To misrepresent other people’s arguments by making their argument worse is a fallacy called the “straw man.” However, to misrepresenting someone’s argument by improving it isn’t wrong. Rather than argue against a flawed argument, we should want to argue against the best argument we can.
Supporting evidence, relevance, considering all viable options, and charity are essential for any good argument. People all too often fail to live up to these standards, and such standards are difficult to live up to without experience. People with no experience with logic have an even greater chance of providing us with inappropriate supporting evidence (non-arguments), overly ambitious conclusions, red herrings, false dilemmas, and straw men.
For more information on fallacies, you might like: