When I was in fourth grade one of my friends regularly regaled me at recess with amazing stories of his fleet of remote controlled model airplanes. These were incredible little aircraft, each with video cameras that transmitted back to his hand-held remote control so he could have a first-person view of the flight from the plane. While streaming video is expected in today’s toy drones, it was mind-blowing for me in 1981. Some of my friend’s model airplanes even had BB guns he could target remotely at squirrels as he flew them over his parents’ fields.

My friend Dave was a good storyteller and I believed his amazing stories when I was in the fourth grade, at least until they grew a bit too far-fetched. (You can ride these model airplanes?) He finally pulled the rug out from under me during one recess story session. For having believed any of his stories I felt like Charlie Brown with the wind knocked out of his lungs as he lands flat on his back after Lucy pulls the football away.

Since then, I’ve worked to improve my critical faculties of judgement a bit. As a credulous person prone, like all of us, to believe reflexively, I’ve found it prudent to adopt a few epistemic axioms to hold in mind in order to avoid believing absurdities. Hereunder I present a first pass at my preferred filters for disbelieving foolishness.

  • Bayes’ bet: “Posterior probability is proportional to prior probability times observed evidence likelihood.” While Bayes and his successors have developed an extraordinarily useful mathematics of probability from his rule and theorem, even a verbal understanding of his argument has utility. Belief should be held with only the degree of confidence its ascertainable probability confers upon it and should be subject to change based on the likely truth of new evidence.
  • Sagan’s standard: “Extraordinary claims require extraordinary evidence.” A special case of Bayes’ bet. Given limited cognitive resources, not every claim may be evaluated to determine whether it passes a threshold of probability sufficiently approaching certainty to be accepted as true. Claims consistent with already justified claims may be accepted with less scrutiny than those unsupported by or in contradiction with already justified claims, as their consistency grants them a greater probability of being true. Conversely, claims significantly at odds with previously justified claims have a lower probability of being true and should be rejected unless supported by multiple, independent sources of evidence. 
  • Hume’s Hammer: “No testimony is sufficient to establish a miracle unless the testimony be of such a kind that its falsehood would be more miraculous than the fact which it endeavors to establish.” Another special case of Bayes’ bet as applied to eyewitness testimony of the supernatural. It is far more likely, given the weight of daily evidence for the operation of nature as understood through its laws, that a reported violation of those laws be given in deceit or by the deceived.
  • Hitchens’ hatchet: “What can be asserted without evidence can be dismissed without evidence.” Another Bayesian corollary, this one emphasizing that the burden of proof is on the claimant. Were it not, then one would be obligated to credulously accept any utterance without justification, leading to belief in any arbitrary proposition. Psychological research indicates that this is pretty much what the unconscious mind does all the time, so it’s a really good idea to think twice.
  • Occam’s razor: Entia non sunt multiplicanda praeter necessitatem. (“Entities should not be multiplied unnecessarily.”) Among competing hypotheses offering equal explanatory power, the one requiring the fewest assumptions should be adopted. As the likelihood of error increases with complexity, the principle of parsimony directs one to choose the explanation positing the fewest hypothetical entities. As Einstein said, “Everything should be made as simple as possible, but not simpler.”
  • Bacon’s burden: Francis Bacon observed that “The human understanding when it has once adopted an opinion (either as being the received opinion or as being agreeable to itself) draws all things else to support and agree with it.” Modern psychology calls this tendency of our minds to seek and favor information evidence confirming that which we already believe and dismiss evidence for that which we do not the confirmation bias. Given knowledge of this bias, we should each take up Bacon’s burden by being objective in evaluating evidence contrary to one’s already held beliefs to avoid the traps of premature, dogmatic, cognitive closure and willful ignorance.
  • Voltaire’s verity: “A witty saying proves nothing.” lrony aside, clever catch phrases and pretty polemics count for naught. We are easily seduced by what merely sounds good, by surface explanations, by easy answers. As H.L. Mencken said, “there is always a well-known solution to every human problem — neat, plausible, and wrong.” To be valid, conclusions must be logically connected by rules of inference to premises sufficiently justified by evidence.
From the classic fallacies of logical inference to the recently uncovered, scientifically validated cognitive biases, to the more subtle self-deceptions such as the Ludic and Narrative fallacies revealed by thinkers like Nassim Nicholas Taleb, there are dozens more epistemic axioms that I should add to my collection to provide even minimal protection against the frailty of the human mind. Since cognitive fatigue (another epistemic evil!) has set in, I’ll trail off for now with the awesome Existential Comic apropos of today’s topic …

What are your hard-won epistemic axioms?