Ethical Realism

February 25, 2010

Four Types of Justification

Whenever we provide an argument we should provide some justification for any controversial premise that our argument requires everyone to accept. We need to answer the question, “Why should anyone agree?” I will discuss four kind of justifications and the corresponding fallacies:

  1. Appeal to Authority
  2. Argument from Analogy
  3. Generalization
  4. Personal Experience

1. Appeal to Authority

We don’t always have the time to find out every fact about the universe through scientific experimentation. Instead, we accept the knowledge of others. This is especially important when we want to know about science or technology. For example, we know that eating too much fatty food tends to be unhealthy. We can rely on expert opinion as long as the experts agree and arrived at their opinions through a reliable method.

If experts arrived at their opinions through a reliable method and they agree, then we have a great deal of reason to agree with them. If an expert knows much more than we do about something, then we might have no choice but to take their opinion seriously. The relevant opinions of experts aren’t beliefs we necessarily have to agree with, but they are worthy of consideration (and permissible to hold), even when the experts disagree. For example, scientists aren’t sure if string theory is true. Therefore, we have good reason to be uncertain about what to think on the subject. It seems plausible to think that it can be rational to believe that string theory is true or to reject it as false.

Appeal to Inappropriate Authority

It is inappropriate to cite an authority when (a) the person is not an expert (of the topic in question), (b) the experts disagree, or (c) the experts are unable to form a reliable opinion. For example, doctors are generally not experts in philosophy, so their philosophical opinions are not particularly relevant to any philosophical debate. When people cite an authority in order to support their argument in the wrong way, they are using a fallacy known as the appeal to inappropriate authority.

An obvious example of an appeal to inappropriate authority is the following:

  1. Sylvia has no expertise in ethics or law, but she went to war, and she says that capital punishment is immoral.
  2. Therefore, capital punishment is immoral.

2. Argument from Analogy

Analogies are often useful to help us justify our arguments. Analogies are comparisons between two things that reveal some relevant similarity about those two things. For example, punching people and kicking people are both generally wrong for the same reason—they hurt people. So, punching and kicking are analogous in that sense.

One example of an analogy in philosophy is Peter Singer’s comparison of saving a drowning child in a small pool of water and saving lives through charity. He argues that both forms of behavior are moral obligations because we can do a great deal of good at little cost to ourselves.

False Analogy

Analogies don’t always work. To use an analogy to support an argument when the analogy doesn’t reflect the relevant similarities is a fallacy known as a false analogy. Some people think Peter Singer’s analogy is fallacious, but that is a contentious issue. An obvious example of a false analogy is the following:

  1. The death penalty and murder are both analogous insofar as they kill people.
  2. It is wrong to murder someone.
  3. Therefore, it is probably wrong to have the death penalty.

The problem with this argument is that we know it is sometimes wrong to kill someone, but it might also be morally acceptable to kill others in certain extenuating circumstances. The death penalty might be one of the few times that killing a person can be morally acceptable.

3. Generalization

Generalization is essential for just about any justification to work. For example, we assume that the past will be like the future in certain ways. The Sun will rise tomorrow. Eating lots of fatty foods will still be unhealthy two days from now. And so on.

In particular, it seems rational to assume that the world will continue to be predictable in the future insofar as the laws of nature will remain the same. The law of gravity will continue to exist, the causal processes we interact with will continue to exist, etc.

Hasty Generalization

However, there are various ways generalization could be inappropriately applied. One common failure of generalization is the hasty generalization fallacy. We need a sufficiently large sample size before we can generalize. For example, fatty foods have always been unhealthy, so we think they always will be.

A common result of reasoning with a hasty generalization is racism. People who have had some bad experiences with people of a certain racial group sometimes decide that everyone of that racial group has various negative traits. However, each of us has a very unique and limited experience of the world and we shouldn’t judge a group of people based on a handful of experiences.

An obvious example of the hasty generalization fallacy is the following:

  1. The last two weeks that I ate chocolate were also weeks that I lost weight.
  2. Therefore, eating chocolate probably causes people to lose weight.

4. Personal Experience

One of the most common types of justification is personal experience. We know other people have thoughts in part because we personally have thoughts. We think they see the color green in part because we see the color green. Personal experience is an important factor in justification despite the fact that it requires a unique and limited experience of the world. Personal experience can be combined with generalization and observation to know that others have similar personal experience to our own.

For example, we experience that pain feels bad and that touching fire causes us pain. It is not such a leap to realize that other people don’t want us to burn them with fire because pain also feels bad to them.

Anecdotal Evidence

Personal experience is often misused in justifications, which is known as the anecdotal evidence fallacy. What people call testimonial evidence tends to be used as a form of anecdotal evidence to argue that something is true for me and so it must be true for others as well (without the appropriate generalization or observations involved). For example, the fact that a drug works for us doesn’t mean it will work for others.

We see the anecdotal evidence fallacy on television every day. People always say, “If I can do it, so can you!” Or “It worked for me, so it will work for you!” There is no way to know this without a scientific study and relevant data.

An obvious example of anecdotal evidence used in an argument in the following:

  1. Several people got healthier after wearing one of these bracelets I sell.
  2. Therefore, these bracelets I sell probably make people healthier.


We need to try to justify our arguments appropriately. To justify an argument appropriately seems rare in everyday life, so we should give our justifications a lot more thought and consideration. It might not be possible to always justify our arguments perfectly, but we can get better with experience.

(Updated 11/24/2013)


  1. […] the question to to some degree is extremely common because people generally don’t know how to justify their arguments. An inappropriate appeal to authority, false analogy, hasty generalization, and anecdotal evidence […]

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  2. […] good arguments are. In particular, (i) formal logic, (ii) requirements of good arguments, (iii) justification, and (iv) terrible ways to […]

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