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Critical thinking is not a single activity. It is a complicated, complex, and imperfect approach to information processing and decision-making. Even really good critical thinkers make errors in thinking. Since practice makes permanent, to be good critical thinkers we must first ensure that our processes are correct, and then practice these skills regularly. We can do this by:

• Separating our thoughts from our feelings by identifying the biases and values we use to interpret information, bearing in mind that all of us (even experts) make conclusions and decisions influenced by biases and personal values.

• Relying on experts for information that we cannot hope to access on our own, and by evaluating the source of their expertise before we put our trust in them.

• Recognizing when we are acting in a superstitious way and attempting to overcome unfounded superstitious beliefs.

• Understanding the limitations and misuse, malicious or not, of statistics before relying on them as evidence (of anything).

• Avoiding forcing our thoughts and ideas into arbitrary groupings. For example, we chose not to have a seven-day critical thinking week, because a) we had more than seven things to say, and b) we don’t know of any reason why a week should have seven days.

• Being open to changing our mind. Critical thinking, like science, should be self-correcting. New information should change how we think about an old subject. Changing our mind might be the most difficult, and smartest thing we do.

We hope you have enjoyed our week(ish) of critical thinking and perhaps learned something new. Please apply our critical thinking framework to your decision making. It really is the “one-size fits all” solution to many of the world’s problems. And please, keep the discussion going. CFIC welcomes your suggestions for tools that help with critical thinking. We are happy to accept contributions to our (virtual) Critical Thinking Library (coming soon) and Critical Links newsletter (see our submission guidelines), or you can join in the conversation on social media.

For more information about critical thinking, please listen to Podcast for Inquiry’s David Robert Grimes on his book, Good Thinking.

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Discussion:

What are other topics we should have included in our Critical Thinking week(ish)? What was one thing you learned or were reminded of during the week? What are some ideas for more broadly sharing Critical Thinking information?

Astute readers who are still following this series have no doubt noticed that our ‘week(ish)’ has reached its 10th day. Since examining underlying assumptions is a crucial component of critical thinking, we have decided to challenge our readers’ concept of what a week is.

Of course, seven days is the current conventional designation for the length of a week, but there is no physical basis for this unit, unlike the day (Earth’s rotation), or year (Earth’s revolution around the Sun). Indeed, ancient civilizations had a variety of week-lengths: The Egyptians used 10 days, the Etruscans eight, while the Babylonians decided on seven weekdays that they named for the Sun, the Moon, Mercury, Venus, Mars, Jupiter, and Saturn (names that much of the world still uses today). Though it is an inconvenient fact that the timing of the day, lunar month, and year cannot be described with round numbers or simple mathematical relationships, the seven-day week at least had the advantage of (almost) being a quarter of the 27.3-day lunar cycle. 

A more recent suggestion was the French Republican Calendar, established in 1793. The intention was to replace the religious names and connotations of the Gregorian calendar with a secular, scientific, and rational system. This calendar had 30-day months, divided into three weeks with ten days: primidi, duodi, tridi, quartidi, quintidi, sextidi, septidi, octidi, nonidi, décadi. This calendar was abandoned by Napoleon in 1806. Most of the world has adopted the metric system of measurement (which also came out of the French Revolution), but there has been no appetite for implementing a similar reform to our calendar standards.

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Discussion:

Why do we (still) have the seven-day week? Is it worth the effort to try to get rid of it? 

The eighth installment in the Critical Thinking Week Series

One of the requirements for being an effective critical thinker is having the practice of continually re-examining one’s position(s), and taking an attitude of humility, being ready, willing, and able to revise an opinion based on the best available evidence.

Rational thinking entails starting with premises and evidence-based data, and then using appropriate argumentation techniques to develop a position (or justify a claim), based on the data and evidence. But if there are errors in the data (accidental or deliberate), or flaws in the argument, the conclusions are called into question, and the argument will need to be re-evaluated.

Critical thinkers must be critical of their own thoughts. As Richard Feynman said, “The first principle is that you must not fool yourself — and you are the easiest person to fool.”

“I don’t think I’m always right, but I always think I’m right” —Don Loeb

When a person becomes overly committed to a belief, they may begin to reject all input contrary to that belief, only accepting information supporting it. To be a true critical thinker, one has to listen to contrary arguments and evaluate them thoroughly, being open to the possibility that these new arguments may change one’s perspective. 

In 2023, more than 10,000 research papers were retracted. Of course, retractions rarely receive much publicity, but websites such as Retraction Watch stand on guard for good science. A crucially important process of the development of scientific knowledge is being able to identify and learn from missteps and mistakes. On the other hand, it is human nature to try to avoid the embarrassment of being wrong. Kudos to those who have the courage to publicly admit their errors, accept the consequences (if there are any), and do the next right thing. Here are a few examples of scientists taking this admirable action.

For more information, you might also enjoy the Podcast for Inquiry episode, The Ancient Art of Thinking for Yourself, with Robin Reames.

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Discussion:

Have you made a rational decision to change your mind on an important question or issue? What caused you to do this? What consequences did you face?

Part 6 of the 2025 Critical Thinking Week Series

There may be no other human construct quite like statistics. In a stroke of a pen or click-clack of a keyboard, something can be created that looks and acts like a statistic. However, for most of us, our understanding of the study of statistics is only a tiny fraction of that of a statistician. This is true regardless of the depth of our knowledge, and regardless of whether the statistic is a complete fabrication or a highly accurate, reliable, and valid report. 

Validity: Does the experiment measure what it is supposed to measure?

Reliability: Are the results consistent and replicable?

Accuracy: Are the measurements true?

Even when data is highly reliable, accurate, and valid, statistics can be used to mislead the user. 

Correlation does not imply causation: Most people have heard the term “correlation does not imply causation” and yet continue to confound the two terms. For example, 100 percent of people who drink milk die. More seriously, however, is the erroneous belief that vaccines cause autism. Because autism is diagnosed at approximately the same time that childhood vaccines are given, people make the connection and assume causation. However, since until recently, almost every child was vaccinated. It stands to reason that almost every child who gets autism was vaccinated, but there is no increase in the rate of autism between the vaccinated and unvaccinated children.

For other wildly amusing examples of non-causal correlations, see Spurious Correlations.

Meaning of statistics: Before declaring statistics to be useful, it is important to also consider what they actually mean. Think of the following claims:

• “We’ll help you save 20 percent more than the competition.”
• “Drug X will reduce your risk of heart attack and stroke by 50 percent more than Drug Y.”
• “Drug A will increase your risk of an adverse event by 5 percent compared to Drug B.”

There is missing critical information in interpreting these claims. 

• Baseline information: What is the baseline for the decreases and increases? If you have a 1 in 1000 chance of suffering a heart attack (0.01 percent chance) and a drug will reduce the risk by 50 percent, you will now have a 0.005 percent chance. The 50 percent reduction is real, but is not significant to most people. In contrast, if you have a 1-in-2 chance of suffering a heart attack, this claim means that your risk is reduced from 50 percent to 25 percent.

In other words:

• Drug X may be reducing the risk of heart attack and stroke from 75 percent this year to 25 percent, if you’re looking at an absolute risk reduction of 50 percent. But more likely, someone’s risk of heart attack and stroke is being reduced from two percent to one percent, which is also a 50 percent decrease, but only relatively better. 
• Drug A may increase the risk of an adverse event from 10 percent to 15 percent, a 5 percent absolute increase. But more likely, someone’s risk is increasing relatively from 10 percent to 10.5 percent, a 5 percent relative increase.

This is how marketing works. It takes advantage of our reliance upon, and widespread inability to properly interpret, statistics. But it isn’t just those driven by the Friedman Doctrine who misuse statistics. We must hold ourselves and those we trust to the standard of properly representing statistics. Demand of everyone, everywhere, and every time that the baseline rates and probabilities, and whether relative or absolute differences, are being reported.

For more information: See CFIC’s 2010 presentation, “The Curious World of Probabilities with Professor Jeffrey Rosenthal.”

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Discussion:

What statistics have you relied on and later learned were faulty? What are other ways that statistics can be misleading?

Much of the strife in the world today boils down to people having, and sharing, unshakeable thoughts and ideas. Conversation becomes a battle to prove oneself right and others wrong. Many otherwise critical thinkers are of the opinion that if everyone thought critically about the same thing, they would each come to the same (correct) conclusion. This belief ignores the fact that each of us perceives “correctness” based on what we value.

For example, when choosing good economic policy, are we seeking the economic policy that benefits us personally, the one that is good for the geographic area we live in, or the one that spreads the wealth broadly and fairly around the world? When contemplating good healthcare spending, do we value saving lives, minimizing infirmity, or increasing life expectancy?

Critical thinking includes being open to hearing others’ ideas and striving to understand their perspectives. A good conversation that seeks to understand rather than change minds is the key to good critical thinking. Provided both parties agree that it’s OK to believe (and value) different things, people with contrary opinions can have good conversations and remain friends. The Conversation offers some great tips on improving conversation when we disagree. 

All ideas grow out of other ideas. —Anish Kapoor

If your dignity hinges upon your (perceived) intelligence, it may often be tempting to believe that you are right and everyone else is either misinformed or unintelligent. Critical thinkers must avoid this temptation. In fact, even among very learned people, there are differences of opinion. Sometimes there is no “right” solution, only a better solution for your value system. Learning to disagree without being disagreeable (or judgemental) — the humility in seeing the validity of diverse conclusions — is the key to a more civil and democratic society.

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Discussion:

What have you learned from someone with a different perspective? Did it change your perspective?