Some guidelines

These eleven rules are known as Prospero’s Precepts and can serve as a general-purpose guideline for critical thinking:


All beliefs in whatever realm are theories at some level. (Stephen Schneider)

Do not condemn the judgment of another because it differs from your own. You may both be wrong. (Dandemis)

Read not to contradict and confute; nor to believe and take for granted; nor to find talk and discourse; but to weigh and consider. (Francis Bacon)

Never fall in love with your hypothesis. (Peter Medawar)

It is a capital mistake to theorize before one has data. Insensibly one begins to twist facts to suit theories instead of theories to suit facts. (Arthur Conan Doyle)

A theory should not attempt to explain all the facts, because some of the facts are wrong. (Francis Crick)

The thing that doesn’t fit is the thing that is most interesting. (Richard Feynman)

To kill an error is as good a service as, and sometimes even better than, the establishing of a new truth or fact. (Charles Darwin)

It ain’t what you don’t know that gets you into trouble. It’s what you know for sure that just ain’t so. (Mark Twain)

Ignorance is preferable to error; and he is less remote from the truth who believes nothing, than he who believes what is wrong. (Thomas Jefferson)

All truth passes through three stages. First, it is ridiculed, second, it is violently opposed, and third, it is accepted as self-evident. (Arthur Schopenhauer)

Heading into Battle

An argument is not a fist fight. If you are thinking in terms of winners and losers, you already lost. Beating people into submission to our point of view is not effective for very long. Shouting, sarcasm, ridicule, mockery—these things can shut down a rational discussion quickly. Our goal is to open the discussion up to a variety of points of view and remain calm about them. Our interest is not winning but instead working together to solve a problem or arrive at an understanding.

We need to assume that people preparing to discuss an issue are relatively rational at the outset and hope they are assuming the same thing about us. We also need to take a look at our own mental state and try to predispose ourselves to rational thinking. Are there any unhelpful emotional reactions we’re having that will interfere with clear thinking? Emotional reactions are fine—after all, we’re human and have emotions—but resist falling into the grip of a strong emotion. We want to keep things rational and pragmatic.

Obviously we are deeply connected to our emotions, but our emotions are not us, they’re only a part of us; and we need to keep them in perspective. A lot of people mistakenly believe they are thinking when in fact they are having an emotional reaction. Polarization occurs when someone thinks their interests are in jeopardy, and that is a situation likely to cause an emotional reaction in most of us. The best time to shut down a polarizing situation is to start while everyone is still reasonable.

Perspective-6 or 9

Just because someone disagrees with you does not make them stupid. It is possible for intelligent people to look at the same set of facts and come to differing conclusions. One of the most effective ways to defuse polarization is to determine what everyone agrees on. When things start to get a little heated, make a list of the areas of agreement. Identify the areas where there is no dispute. This can help people feel less threatened.

Do we have the facts? Have we clearly identified them and separated them from other sorts of statements, like statements of belief or opinion? Are there any cognitive biases that are twisting or distorting the information? The great thing about a statement of fact is that it is independently verifiable. What that means is that you can find out facts for yourself without resorting to hasty assumptions or relying on someone else for information. If I say it’s raining right now, you don’t need an interpreter or an expert to determine if I’m being factual, you can look for yourself. If you’re having trouble agreeing on a statement or claim, then there’s a fair chance the statement is not a statement of fact.

The next step in keeping things rational is to determine which particular statements are causing problems. What makes those statements problematic? Is there appropriate support or evidence for the claims? What is it that feels suspicious and why does it seem questionable? Put things into categories to make it easier to see what you are dealing with.

Another helpful tactic is to specifically identify the issue and then list the kinds of support offered. Underscore the statement that seems to both sum the up issue and present a point of view about it. Locate and examine the support for the claim. Support can be such things as facts, expert testimonials, statistics, examples, concrete details. Is the support sufficient and convincing, or is more support needed?

Identifying the facts. Assessing the support. Rooting out cognitive bias. Establishing the facts. These steps are essential in any rational discussion, but the one thing we have a tendency to overlook is ourselves and our own limitations. Once we fully understand that there are limits to our own thinking abilities, we’re more likely to be tolerant of the limitations of others.

Evaluating Claims Quiz: the Answers

Spoiler Alert: below are the answers to the statements from the Evaluating Claims Quiz. Don’t read the answers before you take the quiz. I’ll give you the short explanations here. If you want more detailed explanation of any of these statements, please let me know.


1. There is an external reality that is independent of our representations of it.

This is true. It’s why you can be sure you are real, not part of a computer simulation nor a brain in a vat. What you are experiencing with your sensory apparatus is reality and not a dream; however, your sensory apparatus doesn’t always give you an accurate picture and there is much our senses can’t detect.

2. When evaluating a claim, look for disconfirming as well as confirming evidence.

We tend to favor evidence that supports our view and ignore evidence that refutes it. This is called confirmation bias or cherry-picking. If you can’t find evidence that refutes your claim, you probably aren’t looking hard enough. We must deal with all of the evidence, even evidence we don’t feel very happy about.

3. We should accept an extraordinary hypothesis only when no ordinary one will do.

This is true, too. You may have heard it expressed in this way: extraordinary claims require extraordinary proof. This idea also is related to a concept called “Occam’s Razor” which exhorts us to keep things simple.

4. If we have no reason to doubt what is disclosed to us through perception, introspection, memory, or reason, then we are justified in believing it.

Also true. However, there are some pitfalls when it comes to trusting our sensory appartus, our memory, and our reason; and we need to guard against those pitfalls. We know that all of these paths to knowledge are prone to error and must be double-checked against other sources of information.

5. It is reasonable to accept personal experience as reliable evidence only if there is no reason to doubt its reliability.

True again, with the same cautions as above. Your personal experience should not be unique but rather a reflection of the common experience of others.

6. The more background information a proposition conflicts with, the more reason there is to doubt it.

True. This may seem self-evident. When a claim runs counter to its context, you have a problem.

7. When there is good reason to doubt a proposition, we should proportion our belief to the evidence.

It’s all about the quality of the evidence. Evidence can range from scientific studies to divine revelation. Be prepared to explain why you accept some evidence as good support for an argument and reject other evidence as insufficient.

8.  There is good reason to doubt a proposition if it conflicts with other propositions that we have good reason to believe.

This relates to one of the Theories of Truth known as the Coherence Theory. The statement we are examining is true if it fits with other statements we know to be true. The statement is coherent because it “sticks together” with the other things we know.

9. There is good reason to doubt a proposition if it conflicts with expert opinion.

Americans seem to have a love/hate relationship with experts. Since the founding of the republic we have relied on them and resented them. Think of the anti-vax movement (those parents who endanger the rest of us because they believe vaccinations will cause autism in their kids). When the experts are in agreement, they’re almost always right. Analysis of the data gives us little reason to doubt the experts, so long as you are sure they really are experts.


Let me know if you have questions about any of these.

Evaluating Claims: A Quiz


POP QUIZ–See if you understand some principles of critical thought. You can find lots of lists similar to these. The scientist Carl Sagan said his list could be put to use as a bulls*t detector.

True or False?

1._____There is an external reality that is independent of our representations of it.

2._____When evaluating a claim, look for disconfirming as well as confirming evidence.

3._____We should accept an extraordinary hypothesis only when no ordinary one will do.

4._____If we have no reason to doubt what is disclosed to us through perception, introspection, memory, or reason, then we are justified in believing it.

5._____It is reasonable to accept personal experience as reliable evidence only if there is no reason to doubt its reliability.

6._____The more background information a proposition conflicts with, the more reason there is to doubt it.

7._____When there is good reason to doubt a proposition, we should proportion our belief to the evidence.

8._____There is good reason to doubt a proposition if it conflicts with other propositions that we have good reason to believe.

9._____There is good reason to doubt a proposition if it conflicts with expert opinion.


Her Truth, your Truth, my Truth— whose Truth?

We need to pay close attention to short words that name big concepts. These words are often capitalized, words like Justice, Freedom, Love, Beauty, Duty, Honor, Judgment, Wisdom. Truth is one of those big concepts, and we need to be careful about how we use the word. I’m hearing a phrase used more and more frequently that is worrying me because it seems to stretch and distort the meaning of truth.


The problem shows up in these kinds of constructions: She’s sharing her truth, he’s living his truth or that’s my truth. It’s the possessive pronoun that is the source of concern. Truth doesn’t belong to any of us. Or to put it more precisely, truth belongs to all of us because one of the prime characteristics of truth is this: if it’s true, it’s true for everybody. Truth is public.

This may seem like nit-picking to some, but one key characteristic of critical thinking is clarity. There are excellent reasons to be clear with this word rather than ambiguous. In the 20th Century, we saw a number of examples of what can happen when people think they are in possession of truth. These are the people who create human tragedies of the worst magnitude. If you are in close contact with someone who believes they own truth, then you may want to put a lot of distance between the two of you before the war crimes trials start.

Truth has three characteristics that must be present in order for us to be sure we’re dealing with truth and not something else. As we’ve seen, one characteristic is that
truth must be public—the same for everyone. The other two characteristics are that truth is independent and it is eternal. A clear understanding of these three words helps us avoid the sort of definitional dispute that goes on in a college dorm hallway until three in the morning. Definitional disputes can be a waste of time because we have a ready authority standing by to help: the dictionary. A useful discussion ends when we are not clear about the meaning of the words we are using.

And so:
Truth is public. If it’s true for you, it’s true for everybody, or it isn’t true.
Truth is independent. In other words, truth is true whether you believe it or not. It is not dependent on what you happen to believe is true.
And Truth is eternal. That’s to say if the claim being made is true, then it will continue to be true ten years from now. The claim remains true in its context, and nothing will come along to change it. If it is true that it is 60 degrees outside today, then ten years from now it still will have been true that it was 60 degrees today.


It may be helpful to think of truth as a journey rather than a destination. I feel more comfortable with people who say they are moving closer to the truth than I am with people who seem to say I’ve arrived at the truth and it’s mine. Political views, identity issues, statements of belief are not necessarily true unless they meet the three characteristics we mentioned: public, independent and eternal. I think that in the case of constructions like her truth what is meant is not truth but experience. Still, it seems the phrase her truth has greater rhetorical resonance than the phrase her experience. Which is why I suspect I’m fighting a rising tide. It may some day be true that the words truth and experience are synonyms, but it isn’t true yet.

Why do smart people make misteaks?

Neuroscience researchers are intrigued by the idea that we have two primary ways of thinking: one guided by encoded evolutionary info controlling our fight or flight response to stimulus and one that is guided by principles of rationality and reason. Most people think they are using thinking style two–being rational, disciplined, deliberative. The fact is, though, that all of us are trapped and victimized by thinking style one often without being aware of it.

brain gears

Style one arose to help us survive, so it is reactive and semi-automatic. It helped us escape danger while moving through the tall grass on the open savanna. It focuses on pattern recognition and response, almost antithetical to the kind of probabilistic thinking we need to thrive in the 21st century. These automatic responses to stimulus create what we call cognitive biases,  habitual ways of thinking that may have helped us survive in the distant past but are no longer useful for meeting today’s challenges.

In fact, cognitive biases are not only unhelpful; they can be dangerous. They can get in the way of rational deliberation and trip us up by causing us to believe we have the right answer when we do not. And these biases often kick in below the level of conscious thought, making them hard to spot.


Here’s a cognitive issue most of us run into on a regular basis: Imagine that I have a ball and a bat for sale. The bat costs $1.00 more than the ball, which costs a nickel. So what do the two items cost together? Most of us jump straight to $1.05 for the two together, but that’s not the answer. That’s how much the bat costs. The bat costs $1.00 more than the five-cent ball so the two together cost…

1.05 + .05 = $1.10

And that is the difference between automatic thinking and critical thinking. We’ve been taught to use a heuristic (or rule of thumb) when dealing with word problems: focus on the numbers. Here, though, the heuristic fails us because we aren’t focusing on the numbers themselves, we’re focusing on their relationship to each other.


I recently saw a list of over two hundred cognitive biases put together by Wikipedia, but don’t get disheartened. You don’t have to memorize a long list of terms and definitions. Simple awareness is a good start. Coming up, I will concentrate on a half dozen or so of the most common biases and point out effective ways to check their influence. Look for a discussion of specific biases in a later post. Also, please feel free to let me know about areas of critical thinking that are of special interest to you.


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Craig Butcher is an award-winning educator who has taught critical thinking skills for more than two decades. In addition, he has worked on Capitol Hill as a congressional aide and has been a top-rated broadcaster.