Editing Fallacy (section)

== Formal fallacy ==
{{Main|Formal fallacy}}

A formal fallacy, deductive fallacy, [[logical fallacy]] or ''non sequitur'' ([[Latin]] for "it does not follow") is a flaw in the structure of a [[deductive reasoning|deductive]] [[logical argument|argument]] that renders the argument [[Validity (logic)|invalid]]. The flaw can be expressed in the standard system of logic.<ref name="GenslerAZ" /> Such an argument is always considered to be wrong.
The presence of the formal fallacy does not imply anything about the argument's [[premise]]s or its conclusion. Both may actually be true or may even be more probable as a result of the argument, but the deductive argument is still invalid because the conclusion does not follow from the premises in the manner described.

Even non-deductive arguments can be said to be fallacious: for example, an [[Inductive reasoning|inductive]] argument that incorrectly applies principles of probability or [[causality]]. But "since deductive arguments depend on formal properties and inductive arguments don't, formal fallacies apply only to deductive arguments".<ref name="garns" />

A [[logical form]] such as "''A'' and ''B''" is independent of any particular conjunction of meaningful propositions. Logical form alone can guarantee that, given true premises, a true conclusion must follow. However, formal logic makes no such guarantee if any premise is false; the conclusion can be either true or false. Any formal error or logical fallacy similarly invalidates the deductive guarantee. Both the argument and all its premises must be true for a conclusion to be true.

The term ''non sequitur'' denotes a general formal fallacy, often meaning one that does not belong to any named subclass of formal fallacies, like [[affirming the consequent]].

=== Common examples ===
{{main|List of fallacies#Formal fallacies}}

==== Ecological fallacy ====
An [[ecological fallacy]] is committed when one draws an inference from data based on the premise that qualities observed for groups necessarily hold for individuals; for example, "if countries with more Protestants tend to have higher suicide rates, then Protestants must be more likely to commit suicide".<ref>{{Cite encyclopedia |year=2004 |title=Ecological Fallacy |encyclopedia=Encyclopedia of Social Science Research Methods |publisher=Sage |location=Thousand Oaks, CA |last=Freedman |first=David A. |editor-last=Lewis-Beck |editor-first=Michael S. |pages=293–295 |isbn=978-0761923633 |editor2-first=Alan |editor2-last=Bryman |editor3-first=Tim Futing |editor3-last=Liao}}</ref>

==== Observational interpretation fallacy ====

The ''[[observational interpretation fallacy]]'' is a cognitive bias that occurs exclusively in the medical field, leading to the mistaken interpretation of observed associations as causal relationships, negatively impacting medical guidelines, clinical decisions, and healthcare practices, potentially compromising patient safety.<ref>D'Amico, F., Marmiere, M., Fonti, M., Battaglia, M., & Belletti, A. (2025). Association Does Not Mean Causation, When Observational Data Were Misinterpreted as Causal: The Observational Interpretation Fallacy. ''Journal of evaluation in clinical practice'', ''31''(1), e14288. <nowiki>https://doi.org/10.1111/jep.14288</nowiki></ref>

=== Fallacy fork ===
[[Maarten Boudry]]<ref name=Boudry/> and others<ref>{{Cite book |last1=Eemeren |first1=Frans H. van |title=Handbook of Argumentation Theory |last2=Garssen |first2=Bart |last3=Krabbe |first3=Erik C. W. |last4=Snoeck Henkemans |first4=A. Francisca |last5=Verheij |first5=Bart |last6=Wagemans |first6=Jean H. M. |date=2014 |publisher=Springer |isbn=978-9048194728 |edition=Revised |location=New York |doi=10.1007/978-90-481-9473-5 |oclc=871004444 |author-link=Frans H. van Eemeren}}</ref> have argued that formal, deductive fallacies rarely occur in real life and that arguments that would be fallacious in formally deductive terms are not necessarily so when context and prior probabilities are taken into account, thus making the argument defeasible and/or inductive. Boudry coined the term ''fallacy fork''.<ref name=Boudry/> For a given fallacy, one must either characterize it by means of a deductive [[argumentation scheme]], which rarely applies (the first prong of the fork), or one must relax definitions and add nuance to take the actual intent and context of the argument into account (the other prong of the fork).<ref name=Boudry/> To argue, for example, that one became nauseated after eating a mushroom because the mushroom was poisonous could be an example of the ''post hoc ergo propter hoc'' fallacy.<ref name="Boudry">{{Cite journal |last=Boudry |first=Maarten |author-link=Maarten Boudry |date=2017 |title=The Fallacy Fork: Why It's Time to Get Rid of Fallacy Theory |journal=[[Skeptical Inquirer]] |volume=41 |issue=5 |pages=46–51}}</ref>