The precepts in this group are the rules people have written down for deciding what to believe. They share a purpose, keeping inquiry honest, but they pull in different directions: some tell you where the burden of proof lies, some tell you what counts as evidence at all, and some tell you when to stop simplifying. The skill is knowing which applies.
Where the burden lies
The oldest rule is the Burden of Proof: whoever asserts must supply the evidence. The Sagan Standard, that extraordinary claims require extraordinary evidence, adjusts the burden to how surprising the claim is. Sagan's Baloney Detection Kit turns these into a checklist: independent confirmation, open debate, several hypotheses, and suspicion of arguments from authority. Alder's Razor takes the hardest line: if something cannot be settled by observation, it is not worth debating.
What counts as evidence
A second set concerns the nature of good evidence. Whewell's Consilience holds that independent lines of evidence converging on one conclusion carry more weight than any one line alone. Feynman's Integrity Standard asks researchers to report everything that might count against their result, not only what supports it. Popper's Falsifiability Principle asks that a theory say what would refute it. Peirce's Pragmatic Maxim holds that a concept means the sum of its practical consequences, so a distinction that makes no difference is no distinction.
When to stop simplifying
A third set concerns simplicity, and here the rules deliberately disagree. Lloyd Morgan's Canon forbids explaining animal behaviour by higher mental faculties when lower ones will do, a razor for comparative psychology. Hickam's Dictum, from medicine, answers Occam's razor directly: patients can have as many diseases as they please. The Map–Territory Relation, Korzybski's phrase, warns that every representation leaves something out. Hayek's Pretence of Knowledge applies the warning to economics: a field that adopts the appearance of measurement without its substance misleads more than one that admits its ignorance.
Practitioners' rules
The newest entries come from practitioners rather than philosophers. Ostrom's Law, that an arrangement that works in practice can work in theory, reverses the usual priority and tells theorists to explain successful cases rather than dismiss them. Cowen's Three Laws, that there is something wrong with everything, a literature on everything, and that all propositions about real interest rates are wrong, are an economist's reminder of humility.
Where it applies
These rules are useful whenever a claim needs weighing: in journalism, in medicine, in courts and in everyday conversation. The burden of proof and the Sagan standard decide who must argue first. Consilience explains why scientists trust findings supported by unrelated methods. Hickam's dictum is taught in medicine precisely because Occam's razor can mislead a diagnostician whose patient has two conditions at once. Ostrom's law has changed how economists approach institutions that their models said should not work.
Where it is argued over
Popper's falsifiability is the most debated rule in the group, as a demarcation line between science and non-science, because of the Duhem–Quine problem described in the model essay. The Sagan standard is criticised for leaving "extraordinary" undefined, so that it can be used to dismiss unwelcome findings. Alder's razor is criticised for ruling out questions, such as those in mathematics and ethics, that are not settled by observation but are still worth debating. The Principle of Sufficient Reason and the Uniformity of Nature are foundational assumptions rather than rules that could be tested.
Why it is worth knowing
These precepts are the working rules of anyone who has to decide what to believe, which is everyone. None is sufficient alone, and several contradict each other on purpose. Knowing them as a set lets a reader ask the right question of a claim: who should prove it, what would count as proof, and whether the simplest explanation is really the right one.
The entries behind this essay: Precept in Science & Epistemology. Every subject has its essays on the essays page.