When eleven-year-old Danielle speaks to a world audience from Yad Vashem, Israel’s Holocaust museum and memorial, she talks about the ideas of historian Hannah Arendt.

In her speech, she says,

Thus Danielle’s conclusion is that the Holocaust resulted at least in part from a failure of critical thinking, and she works to advance critical thinking as a way of preventing future atrocities.

Critical thinking is a mindset of questioning ideas and testing them to see if they are true—and questioning actions to see if they are morally right. Instead of just believing whatever they are told, critical thinkers seek to confirm it for themselves. They regularly reflect on their own assumptions and values to see whether they are consistent with their deeper ideas about truth and morality. From the 1920s to the 1940s, there was a major failure of critical thinking in many European societies that resulted in the catastrophic tragedies of World War II. Charismatic leaders told people what they wanted to hear, and without critical thinking, the people believed them. This enabled the rise of totalitarian dictators like Hitler, Stalin, Mussolini, and, later on, Mao Tse-tung.

Today, there is concern about contemporary failures of critical thinking. On the Internet, people can easily choose the content they want to see, and it’s tempting to block out information that goes against one’s worldviews. Moreover, social media now contains “fake news”—deliberately untrue stories meant to mislead people for political purposes. These phenomena can distort public discussion and subvert democratic processes.

First, you should learn more about what critical thinking is, and how to develop it more in your own life:

• Simple animated video¹ explaining a five-step process for thinking critically.
• More detailed article giving you nine strategies² for critical thinking in everyday living.
• Fascinating video³ on how “filter bubbles” can turn your social media feeds into an echo chamber where you only hear opinions that reinforce your existing beliefs.
• How to develop your mental habits in stages⁴ to become a more rational person.
• Some helpful do’s and don’ts for how to criticize your own thinking effectively⁵.
• Collection of TED Ed lessons⁶ on critical thinking.
• Series of videos by the Foundation for Critical Thinking⁷ aimed at explaining critical thinking to younger kids.

Your mental habits are a lot like your diet. Just as exercising and eating healthy foods will make your body strong and healthy, consuming well-founded information from reliable sources will equip you to be a critical, independent, and objective thinker.

Here are some useful principles for maintaining a healthy information diet:

• Draw from diverse perspectives. No single source of information is completely right all the time. Every newspaper, television commentator, blogger, and author has their own strengths and weaknesses. The best solution is to seek out a wide range of contrasting views on important topics. If you see the best arguments for an idea and the best arguments against it, you can make an informed judgment about which arguments are backed up by better logic and evidence.
• Seek original sources. Many factual claims you see online simply aren’t true. Many pundits on television and online make false claims, and there is no “referee” to correct them. So whenever you hear a dramatic statement—an improbable fact, an extreme number, or a surprising explanation—see if you can trace it back to a reliable source. For example, if you read an article from a site called PatriotEagle4USA.com claiming without proof that two million refugees have entered the US from Syria, search on Google for independent confirmation. Is that number reported in respected news sources like the New York Times or Wall Street Journal? Or official government statistics? If not, you should not believe it (for the record, that’s about 100 times the real number).
• Avoid false equivalencies. When you’re thinking critically about what a leader is telling you, you’ll often find that they have made misleading statements. You’ll naturally be tempted to be angry about this, but their supporters will say: “Well, what about the lie that his opponent told?” It’s hard work to figure out the truth, so it can be very tempting to just conclude that all politicians are liars and it doesn’t matter who’s in charge. This is a dangerous lapse in critical thinking. In trying to find who is more trustworthy, remember that not all lies are equivalent. An exaggeration of a true fact (e.g. saying that a policy saved $10 million when it really saved $8 million) is not nearly as bad as fabricating events that never happened at all, or denying provable facts that can be verified with a 5-second Google search. Since nobody in politics is 100% faultless, critical thinking is required to separate the “ordinary lies” from the “big lies” and focus your energy on opposing the most dangerous falsehoods. One of Hitler’s techniques was called the “big lie,” for example blaming all of society’s ills on the Jews.
• Consider alternatives. When you think you’re starting to figure out the truth about something, it’s easy to suffer what’s known as “confirmation bias.” When you see information that supports an idea you already like, your mind naturally wants to accept it. This may lead you to the wrong conclusion. To fight against confirmation bias, you have to make extra effort to consider other possible explanations. For example, if you are an advocate of equal justice for racial minorities, you should be careful about assuming that all unequal outcomes are the result of racism. In each case, ask yourself what role might be played by other important factors like poverty, education, and bad policies. This can make you a more effective advocate against actual racism.
• Take responsibility. Adolf Eichmann’s problem was that he didn’t take any moral responsibility for his actions. As long as his superiors ordered him to do something, he felt that wiped away any guilt for what he was doing. Thinking critically requires taking moral responsibility for what you do and what you say. The best way to avoid going along with injustice is to not pass off your moral choices to anyone else. If something is right, you should be able to explain why it’s right—and if it’s wrong, you should be able to explain why it’s wrong.

To learn more about what happens when lots of people fail to think critically, you should take a look at these short videos:

• An introduction to the history of the Holocaust,⁸ by Yad Vashem in Israel.
• Animated explainer on how Hitler came to power⁹ in Germany.
• A summary of how Mussolini became dictator¹⁰ in Italy.
• An informative video on Stalin’s crimes¹¹ in the Soviet Union.
• A fact-filled video about World War II,¹² from John Green’s Crash Course
• A brief history of ISIS,¹³ which shows what happens when people fail to think critically in modern times.

It is important to practice critical thinking yourself, but Danielle also sets an example of how young people can show leadership. Consider these ideas for how you can advance critical thinking in your wider community:

• Start a club. Bring together a group of friends, neighbors, or classmates, and pledge to help each other become better critical thinkers.
  • Bring in speakers from your area who can talk about critical thinking and rationality. Potential guests include journalists, scientists, judges, or philosophers.
  • Hold debates about controversial issues, and then switch sides. Seeing difficult questions from different perspectives builds your critical thinking muscles.
  • Take an online course together, maybe on rhetoric, the Holocaust, or critical thinking¹⁴.
• Speak out on social media. Some people criticize social media activism as “slacktivism,” saying that it is too easy and doesn’t really make a difference. It’s true that you shouldn’t let online activism replace other efforts to solve global problems, but speaking out on social media can have an important impact.

As humans we are very social creatures and heavily influenced by what we think the other members of our community are doing. When leaders like Hitler and Mussolini came to power, they tried to create the illusion that everyone in society supported what they were doing and saying. This helped suppress critical thinking, because if people don’t hear anyone around them speaking out against an idea, there’s a tendency to think that the idea must be correct.

Because so much of our social lives now take place on social media, by using your critical thinking and speaking out against injustice, you can shift your friends’ perception of what other people in their community think. This can positively influence those around you and make them more likely to think critically themselves. This action can take many forms:

• Starting a blog to express your views.
• Recording videos on YouTube applying critical thinking to important issues.
• Engaging respectfully with people on Facebook and Twitter and encouraging them to use better critical thinking, while speaking out against injustices yourself.
• Volunteer for pro-critical thinking politicians. Don’t let yourself get cynical. Although there are some politicians who try to manipulate public opinion with dubious claims and arguments, there are also many people in politics who are trying to advance critical thinking. Do some research on the politicians in your area, and see if you can find one whose statements show a commitment to truthfulness and critical thought. Even as a student, you may be able to volunteer for them—whether in their campaign office, or knocking on doors in the community to spread their positive message.
• Program tools to teach critical thinking. Apps and games have the potential to make learning fun and intuitive. If you’ve learned programming, you could create a platform designed to help people distinguish fake news from real news, or train their ability to overcome confirmation bias. If you haven’t learned coding yet, see the entry for “How You Can Be a Danielle and Learn to Program Computers from a Young Age.”
• Meet survivors. One of the most powerful reasons to care about critical thinking is the very real human suffering that happens when people don’t think critically. Reading about the Holocaust is sad, but the history gets a completely different emotional power when you talk to someone who actually lived through it. You can arrange to meet with a survivor and bring them to your school¹⁵ so their stories can impact a bigger audience. You should act quickly because the generation of actual survivors won’t be alive much longer.

For more information, please see the following entries in the companion book A Chronicle of Ideas: A Guide for Superheroines (and Superheroes): Hannah Arendt, Banality of Evil.