Resources for Critical Thinking
in the 21st Century

Assembled by Richard Carrier, Ph.D.

Critical thought in the 21st century requires familiarity with traditional skills (of logic, argument, and fallacy-detection-and-avoidance) but also the most relevant aspects of cognitive science and Bayesian reasoning. Both of those new techniques are the centerpiece of the training program at the Center for Applied Rationality (or CFAR) especially in a forward-thinking application (helping people make better decisions in the future), but the same knowledge can be applied to examine past or current claims and beliefs for the possibility of fallacies, biases, or errors, and to protect yourself from both dubious and nefarious attempts at influence or persuasion.

For a complete guide to traditional critical thinking, covering all the standard principles of logic, questioning, and inquiry, see Christopher DiCarlo's How to Become a Really Good Pain in the Ass [print or kindle]. For the following, see my PDF slides and video.

  • The Art of Persuasion: Critical thought requires understanding persuasion. was launched and maintained by David Straker, a multiply-qualified postgraduate expert in persuasive techniques, to provide a panoply of useful lists and taxonomies of methods of persuasion. You need to know the many ways people attempt to persuade or manipulate others, especially when those methods are less than fair, truthful, or accurate. Consider such knowledge a Defense against the Dark Arts. But some of it can also be used for good, to help you reason better, and spot any flaws in the reasoning of others. See Disciplines, Techniques, and Principles for doorways into many different methods of persuasion, and Explanations and Theories for more on why they work. And for honest logical reasoning, of greatest value here are tutorials on Argument and Syllogisms. If you don't know the basic mechanics of logic, the latter is especially helpful, and will get you up to speed.

  • Logical Fallacies: There are several websites with excellent explanations and taxonomies of logical fallacies. Each explains some fallacies that are not in the others, or the same fallacies in different ways, so if you are not sure you understand a fallacy from reading its discussion on one page, you can try reading up on the same fallacy in the other pages. See: Wikipedia List of Fallacies -:- The Fallacy Files -:- The Fallacy Files' Interactive Taxonomy of Logical Fallacies -:- Bo Bennett's Catalog of Logical Fallacies. Bennett's book Logically Fallacious is the best portable resource for a basic intro to logic and an essentially complete encyclopedia of fallacies aimed at the non-expert [print or kindle].

  • Cognitive Science: One thing new to critical thinking in the 21st century is all we've now learned on how badly built our brains are for the purpose of reasoning well. Our natural inborn tools of thought and cognition are clunky, ad hoc, and prone to numerous common and often well-documented errors. You are as much subject to them as anyone else (because your brain is as human as anyone else's), so you need to study and understand these cognitive biases in order to arm yourself against them (to control, compensate, or correct for them in your own reasoning). Think of this as installing a software patch. It is also helpful to know this stuff so you can spot the same biases affecting the reasoning of others and to be armed against when the conclusions even of experts have been affected by them. Study the Wikipedia List of Cognitive Biases, the most comprehensive starting point on this subject available online. Yet even that is not complete. The following resources pick up the slack with authority:

  • Bayesian Reasoning: Finally, although Bayes' Theorem has been around since the 18th century, it has finally come into its due. It is now widely recognized as an essential component of human reasoning. In fact it happens to be the correct mathematical model for all valid empirical reasoning, and as such, it is crucial to understand it, so you can better understand how to detect weak or flawed arguments and build strong and valid ones. I have done my best to explain it (and its applicability to many tasks in critical thinking) for an audience of humanities majors in Proving History (2012) [print | kindle] (no more than primary school math required). I have also arranged an online calculating tutorial [Bayesian Calculator] and provided a video that really brings it down to basics [Bayes' Theorem: Lust for Glory!]. A good brief and basic intro to all statistical and Bayesian reasoning (especially for non-mathematicians) is Thinking Statistically (Uri Bram, 2012) [print | kindle]. For a more advanced but elegant explanation of why Bayesian reasoning underlies all sound scientific reasoning, see Scientific Reasoning: The Bayesian Approach, 3rd ed. (Colin Howson & Peter Urbach, 2005) [print]. But for beginners, it's essential to understand even basic statistical and probabilistic reasoning, and to that end, start with Innumeracy: Mathematical Illiteracy and Its Consequences (Paulos, 1988) [print | kindle], A Mathematician Reads the Newspaper (Paulos, 1997) [print], and Proofiness: How You're Being Fooled by the Numbers (Seife, 2010) [print | kindle]. For basic skills, most of the math you'll ever really need is in Math Doesn't Suck (McKellar, 2008) [print].

  • A Reliable & Consistent Epistemology: Most important is how you know what you know, and what standards and methods you apply to the task of forming reliable beliefs. It's essential that your epistemology be, in fact, demonstrably reliable. See my thorough treatment of that subject (for forming your own reliable worldview) in Sense and Goodness without God [print | kindle] and Peter Boghossian's skillful treatment of the subject (for challenging others to form a reliable worldview) in A Manual for Creating Atheists [pre-order print | kindle edition in the works]. It's also essential that your epistemology be applied fairly and consistently (and thus applied even to your most cherished or certain beliefs, with the same standards you apply to all other claims and beliefs). You should apply the principles in John Loftus, The Outsider Test for Faith [print | kindle], to all beliefs and claims (not just religions, which is only the example Loftus deploys), including moral beliefs, political beliefs, and everything else.

  • For more on applied epistemology see my companion resource on Practical Logic.


The Principles of Critical Thought:

  • Questioning information rather than merely receiving it (trust but verify).
  • Constant skill applied to all knowledge and belief (not to be compartmentalized).
  • Not an exercise; a tool for belief testing and filtering (defense against false beliefs).
  • Must be applied to yourself as well as others (self-question, self-test, self-critique).
  • Not radical skepticism (work out when information is enough to settle a conclusion).

  • Step 1: Check the facts (check multiple sources and evaluate their reliability).
  • Step 2: Check for biases and fallacies (your own and those of others).
  • Step 3: Consider alternative explanations of the evidence and test them.

  • Find the best defenses of either side of a dispute and compare them.
  • Consider your existing background knowledge and endeavor to acquire more of it.
  • Rely on facts & evidence, not assumptions.
  • Update your beliefs when evidence goes against them.
  • Restate all your beliefs as probabilities; then justify those probabilities
    (or change them if you can't).
See also my digital handout Bayes' Theorem and Its Role in Critical Thinking.

[Originally assembled in 2013 as a helpful resource. May be revised over time.]

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