Also Known as: Post Hoc Ergo Propter Hoc, False Cause, Questionable Cause, Confusing Coincidental Relationships With CausesDescription of Post HocA Post Hoc is a fallacy with the following form:1. A occurs before B.2. Therefore A is the cause of B.The Post Hoc fallacy derives its name from the Latin phrase "Post hoc, ergo propter hoc." This has been traditionally interpreted as "After this, therefore because of this." This fallacy is committed when it is concluded that one event causes another simply because the proposed cause occurred before the proposed effect. More formally, the fallacy involves concluding that A causes or caused B because A occurs before B and there is not sufficient evidence to actually warrant such a claim.It is evident in many cases that the mere fact that A occurs before B in no way indicates a causal relationship. For example, suppose Jill, who is in London, sneezed at the exact same time an earthquake started in California. It would clearly be irrational to arrest Jill for starting a natural disaster, since there is no reason to suspect any causal connection between the two events. While such cases are quite obvious, the Post Hoc fallacy is fairly common because there are cases in which there might be some connection between the events. For example, a person who has her computer crash after she installs a new piece of software would probably suspect that the software was to blame. If she simply concluded that the software caused the crash because it was installed before the crash she would be committing the Post Hoc fallacy. In such cases the fallacy would be committed because the evidence provided fails to justify acceptance of the causal claim. It is even theoretically possible for the fallacy to be committed when A really does cause B, provided that the "evidence" given consists only of the claim that A occured before B. The key to the Post Hoc fallacy is not that there is no causal connection between A and B. It is that adequate evidence has not been provided for a claim that A causes B. Thus, Post Hoc resembles a Hasty Generalization in that it involves making a leap to an unwarranted conclusion. In the case of the Post Hoc fallacy, that leap is to a causal claim instead of a general proposition.Not surprisingly, many superstitions are probably based on Post Hoc reasoning. For example, suppose a person buys a good luck charm, does well on his exam, and then concludes that the good luck charm caused him to do well. This person would have fallen victim to the Post Hoc fallacy. This is not to say that all "superstitions" have no basis at all. For example, some "folk cures" have actually been found to work.Post Hoc fallacies are typically committed because people are simply not careful enough when they reason. Leaping to a causal conclusion is always easier and faster than actually investigating the phenomenon. However, such leaps tend to land far from the truth of the matter. Because Post Hoc fallacies are committed by drawing an unjustified causal conclusion, the key to avoiding them is careful investigation. While it is true that causes precede effects (outside of Star Trek, anyways), it is not true that precedence makes something a cause of something else. Because of this, a causal investigation should begin with finding what occurs before the effect in question, but it should not end there.Examples of Post Hoc1. I had been doing pretty poorly this season. Then my girlfriend gave me this neon laces for my spikes and I won my next three races. Those laces must be good luck...if I keep on wearing them I can't help but win!2. Bill purchases a new PowerMac and it works fine for months. He then buys and installs a new piece of software. The next time he starts up his Mac, it freezes. Bill concludes that the software must be the cause of the freeze.3. Joan is scratched by a cat while visiting her friend. Two days later she comes down with a fever. Joan concludes that the cat's scratch must be the cause of her illness.4. The Republicans pass a new tax reform law that benefits wealthly Americans. Shortly thereafter the economy takes a nose dive. The Democrats claim that the the tax reform caused the economic woes and they push to get rid of it.5. The picture on Jim's old TV set goes out of focus. Jim goes over and strikes the TV soundly on the side and the picture goes back into focus. Jim tells his friend that hitting the TV fixed it.6. Jane gets a rather large wart on her finger. Based on a story her father told her, she cuts a potato in half, rubs it on the wart and then buries it under the light of a full moon. Over the next month her wart shrinks and eventually vanishes. Jane writes her father to tell him how right he was about the cure.A famous cultural example of this is in the Alfred Hitchock movieThe Birds. In that movie, a woman visits a small town. While she is there, the birds in the town suddenly start attacking the people. Briefly, there is talk that since it never happened before she came, she must have caused it.

Fallacy: Post/Cum Hoc Ergo PropterHocDefinition: Post hoc ergo propter hoc: An argument that concludes that a causal relationship between two phenomena exists because one occurred after the other.Cum hoc ergo propter hoc: An argument that concludes that a causal relationship between two phenomena exists because they occur together.Both types essentially equate correlation with causation.Form:Post hoc ergo propter hoc:Premise 1: B occurs after A.Conclusion 1: A causes B.Cum hoc ergo propter hoc:Premise 1: A and B occur together.Conclusion 1: A causes B (or B causes A).Usage:These are among the most prevalent fallacies because of the natural human tendency to seek and establish patterns in the world, even without all of the information that is necessary to do so accurately. As such, I cannot possibly narrow their usage down.Examples:Post hoc ergo propter hoc:1.) Michael prayed for Sarah to recover from her illness. She recovered. Therefore, Sarah recovered because Michael prayed for her to recover.2.) Gas prices rose after President Obama took office. Therefore, President Obama is responsible for rising gas prices.3.) The housing bubble in the United States burst after President Bush took office. Therefore, President Bush was responsible for the burst of the housing bubble.4.) Arthur was depressed. His therapist prescribed medicine for his condition. He felt better after taking the medicine. Therefore, the medicine cured Arthurs depression. (In fact, it was a placebo.)Cum hoc ergo propter hoc:1.) The Earth is warming. This last winter was mild. Therefore, this last winter was mild because of global warming.2.) People who often eat caviar live longer than those who do not. Therefore, caviar increases longevity.3.) We are a more secular society than we were before. We are also more irresponsible. Therefore, secularism leads to irresponsibility.4.) There is still racism in the United States today. On average, black people are poorer than white people in the United States. Therefore, black people are poorer than white people in the United States because of modern racism.Additional Thoughts:Humans are inclined to both pay attention to certain types of patterns and perceive what they want to perceive. Those who understand these inclinations can exploit them. When they do, they often use these fallacies: the media sensationalizes modest scientific studies on correlation, leaping to conclusions about causation in order to get better ratings; politicians casually link themselves to good news and their opponents to bad news in order to instill fear in and gain support from the public; businesses try to make their products seem necessary for happiness. Of course, we can fool ourselves as well, particularly when we become attached to our beliefs and, due to confirmation bias, see only the evidence that supports them.But whether we are fooling ourselves or being fooled by others, these fallacies are the most dangerous when applied to the most complex systems. If understanding system A requires an analysis of 10 variables while understanding system B only requires an analysis of two, it is worse to pick and run with one variable for system A, since one ends up ignoring more variables.Economics stands out as a field in which we should be extraordinarily careful about our analyses and open-minded towards others. There is an indeterminable number of variables involved such that economic comparisons to previous eras (or sometimes even previous days) or other countries are inevitably quite incomplete, if not exercises in futility. Furthermore, we do not want to endlessly experiment on our own economy, since that could put the lives and well-being of millions of people at risk. Yet one need only go to a library, watch the news, or participate in a forum on economics to find people, from the unknown to the most famous, claiming that everything of importance in economics hinges upon a single variable X, as evidenced by a simple correlation. (Attempts to pin the financial crisis of 2008 on the Community Reinvestment Act stand out.) They have their charts and graphs and quotations from great thinkers, but they frequently neglect to address the variables over which others obsess, even going so far as to deny their relevance altogether. And the layman increasingly likes to think that he is an expert because he, too, can see patterns in data, no matter the subject.What we see here is but one case of arrogance and an effective rejection of the scientific method in favor of personal dogma and ignorance. The post hoc and cum hoc fallacies are bad enough on their own, but when people who should or do know better claim to have made a science out of them and when the most ignorant of a subject fancy themselves experts because they can use them, we have a real problem. I have long supported mandatory classes on logic and fallacies, but we would go far simply by eliminating these two fallacies from our arguments.

Post Hoc FallacyExplanationThe Latin phrase post hoc ergo propter hoc means, literally, after this therefore because of this. The post hoc fallacy is committed when it is assumed that because one thing occurred after another, it must have occurred as a result of it. Mere temporal succession, however, does not entail causal succession. Just because one thing follows another does not mean that it was caused by it. This fallacy is closely related to thecum hocfallacy.Example(1) Most people who are read the last rites die shortly afterwards.Therefore:(2) Priests are going around killing people with magic words!This argument commits the post hoc fallacy because it infers a causal connection based solely on temporal order.Real-World ExamplesOne example of the post hoc flaw is the evidence often given for the efficacy of prayer. When someone reasons that as they prayed for something and it then happened, it therefore must have happened because they prayed for it, they commit the post hoc fallacy. The correlation between the prayer and the event could result from coincidence, rather than cause, so does not prove that prayer works.Superstitions often arise from people committing the post hoc fallacy. Consider, for example, a sportsman who adopts a pre-match ritual because one time he did something before a game he got a good result. The reasoning here is presumably that on the first occasion the activity preceded the success, so the activity must have contributed to the success, so repeating the activity is likely to lead to a recurrence of the success. This is a classic example of the post hoc fallacy in action.

Post hoc ergo propter hoc(after this, therefore because of this).This is the fallacy of assuming that A caused B simply because A happened prior to B. A favorite example: "Most rapists read pornography when they were teenagers; obviously, pornography causes violence toward women." The conclusion is invalid, because there can be a correlation between two phenomena without one causing the other. Often, this is because both phenomena may be linked to the same cause. In the example given, it is possible that some psychological factor -- say, a frustrated sex drive -- might cause both a tendency toward sexual violence and a desire for pornographic material, in which case the pornography would not be the true cause of the violence.

Post Hoc or Faulty Causality, or Correlation vs. CausationPost hoc is the shortened version of post hoc ergo propter hoc, which translates as after this, therefore because of this. In other words, the fallacy confuses correlation for causation, or mistakenly claiming that one thing caused another to happen since they happen in sequence.Correlation simply refers to two things happening at the same time, or one thing commonly happening before another thing happens; in other words, the frequency with which one thing occurs corresponds with the frequency with which another occurs. Causation of course means that the one thing occurringcausesthe other to occur.Post hoc refersmistaking correlation for causation. The flaw in the argument is that often a third cause exists, which is causing both to occur frequently, or perhaps the flaw is simply that both things commonly occurregardless of each other.There are a couple key points to understand about this fallacy:First, the fallacy only occurs whenboth things (reasons, premises) have actually occurred; therefore, the fallacy doesnt apply to the future or to debates over whether or not one thing actually occurred. For example, in order to claim that the green-house gasses-global-warming argument isposthoc, you must first agree that a) there is a spike in greenhouse gasses, and b) global warming is actually occurring.Second, most often the fallacy occurs because of a third element that is responsible for causing both of the other elements. So, look for a third cause.Third, reasonable skepticism reveals this to be an incredibly common fallacy in both everyday arguments and in very formal, influential, widely believed, often scientific arguments. For instance, most people recover from their colds a couple days after they take cold medication. But, of course, most people recover from their colds if they take no cold medication whatsoever. Many people get rich when they pray for wealth, but many people who never pray also get rich, and many people who pray to get rich stay poor; also, what about people who pray to other gods and get rich?The danger rests in the degree of skepticism; extreme skepticism will revealall argumentspost hoc, and, in fact, this is the standard argument of most defense lawyers and traditionally all industries when it comes to questions such as cigarettes and lung cancer, safety glass in automobiles, seat belts in automobiles, air bags in automobiles, causes of air pollution, effects of pollution on health and so on; normally scientists provewithin a reasonable doubtcausation decades before the public and those responsible for the cause stop cryingpost hoc. Current, continuing debates overpost hocinclude pretty much every scientific argument that intersects with either faith (evolution, AIDS), industry (global warming) or economic interests.(NPROn The Media 5 minute discussion of this fallacy and flu vaccinations)Fallacy Ex:Drinkers are more likely than non-drinkers to get lung cancer, suggesting drinking causes lung cancer.(It turns out there is a strong correlation between consuming alcohol and developing lung cancer. Thepost hocfallacy would be asserting that alcohol consumptioncauseslung cancer; the actual reason is that people who drink more also tend to smoke, or smoke more, than non drinkers.)Ex: Many claim that marijuana is a gateway drug because those who have smoked marijuana are more likely than those who havent to go on to try other drugs. Thepost hocfallacy would be asserting that marijuana useleads toincreased use of other drugs; the more logical explanation is that those who are willing to try one drug are obviously also willing to try other drugs: the cause willingness to try or use drugs must necessarily existbeforeone tries pot; otherwise, you wouldnt try it in the first place.

Post hoc ergo propter hoc:This is a conclusion that assumes that if 'A' occurred after 'B' then 'B' must have caused 'A.' Example:I drank bottled water and now I am sick, so the water must have made me sick.In this example, the author assumes that if one event chronologically follows another the first event must have caused the second. But the illness could have been caused by the burrito the night before, a flu bug that had been working on the body for days, or a chemical spill across campus. There is no reason, without more evidence, to assume the water caused the person to be sick.Last night at council Ireferred to seeing what I believed was apost hoc fallacyin a report,or more properly apost hoc ergo propter hocfallacy. Yeah, I probably annoyed some folks in the audience because I used Latin words and that confused them. But hey, they already think Im a jerk because I can spell words like egregious and nefarious without using spellcheck, so I doubt I lost any votes over it.It means an error in assigning a causal relationship between two or more coincidental events. For example:1. I combed my hair a different way and I came down with a cold.2. After a few days, Icombed my hair the old way and the cold went away.3. Therefore combing my hair a different way gave me a cold.This is an easy one to see through, but youd be surprised how many people apply this logical fallacy to their thinking. For example, the typical chemtrail conspiracy theory:1. I saw contrails from a plane overhead.2. My skin got itchy afterwards.3. Therefore the government is spraying something from jet planes that is making me sick.Which pretty much sums up the whole nonsense around chemtrails. People naturally look for events that explain what they already believe to be true (confirmation bias).Whencausality doesnot exist between events, what you often find is merely wishful thinking.Post hoc ergo propter hocThe fallacy of Post Hoc Ergo Propter Hoc occurs when something is assumed to be the cause of an event merely because it happened before that event. For example:"The Soviet Union collapsed after instituting state atheism. Therefore we must avoid atheism for the same reasons."This is another type offalse cause fallacy.

Post HocAlias:Post Hoc, Ergo Propter HocTranslation:After this, therefore because of this (Latin)Taxonomy:Logical Fallacy>Informal Fallacy>Non Causa Pro Causa> Post HocSibling Fallacy:Cum Hoc, Ergo Propter HocQuoteSheldon (on phone):Oh, hi mom. The Arctic expedition was a remarkable success, Im all but certain theres a Nobel Prize in my future. Actually, I shouldnt say that. Im entirely certain. No, mother, I could not feel your church group praying for my safety. The fact that Im home safe is not proof that it worked, that logic is Post Hoc Ergo Propter Hoc. No, Im not sassing you in Eskimo talk.UnquoteSource:"The Electric Can Opener Fluctuation",The Big Bang TheoryForms

EventChappened immediately prior to eventE.Therefore,CcausedE.Events of typeChappen immediately prior to events of typeE.Therefore, events of typeCcause events of typeE.

Examples

The only policy that effectively reduces public shootings is right-to-carry laws. Allowing citizens to carry concealed handguns reduces violent crime. In the 31 states that have passed right-to-carry laws since the mid-1980s, the number of multiple-victim public shootings and other violent crimes has dropped dramatically. Murders fell by 7.65%, rapes by 5.2%, aggravated assaults by 7%, and robberies by 3%.[E]vidence shows that even state and local handgun control laws work. For example, in 1974 Massachusetts passed the Bartley-Fox Law, which requires a special license to carry a handgun outside the home or business. The law is supported by a mandatory prison sentence. Studies by Glenn Pierce and William Bowers of Northeastern University documented that after the law was passed handgun homicides in Massachusetts fell 50% and the number of armed robberies dropped 35%.

Source:"The Media Campaign Against Gun Ownership",The Phyllis Schlafly Report, Vol. 33, No. 11, June 2000.Source:"Fact Card", Handgun Control, Inc.

Counter-Example

Roosters crow just before the sun rises.Therefore, roosters crowing cause the sun to rise.

Analysis of the ExamplesExposition:The Post Hoc Fallacy is committed whenever one reasons to a causalconclusionbased solely on the supposed cause preceding its "effect". Of course, it is anecessary conditionof causation that the cause precede the effect, but it is not asufficient condition. Thus, post hoc evidence may suggest the hypothesis of a causal relationship, which then requires further testing, but it is never sufficient evidence on its own.Exposure:Post Hoc also manifests itself as a bias towards jumping to conclusions based upon coincidences. Superstition and magical thinking include Post Hoc thinking; for instance, when a sick person is treated by a witch doctor, or a faith healer, and becomes better afterward, superstitious people conclude that the spell or prayer was effective. Since most illnesses will go away on their own eventually,anytreatment will seem effective by Post Hoc thinking. This is why it is so important to test proposed remedies carefully, rather than jumping to conclusions based upon anecdotal evidence.Source:T. Edward Damer,Attacking Faulty Reasoning: A Practical Guide to Fallacy-Free Arguments (Third Edition)(Wadsworth, 1995), pp. 131-132.Resource:Robert Todd Carroll,"Post Hoc Fallacy",Skeptic's Dictionary.Analysis of the Examples:These two examples show how the same fallacy is often exploited by opposite sides in a debate, in this case, the gun control debate. There are clear claims of causal relationships in thesearguments. In the anti-gun control example, it is claimed that so-called "right-to-carry" laws "effectively reduce" public shootings and violent crime. This claim is supported by statistics on falling crime rates since the mid-1980s in states that have passed such laws. In the pro-gun control example, it is claimed that state and local gun control laws "work", presumably meaning that the laws play a causal role in lowering handgun crime. Again, the claim is supported by statistics on falling crime rates in one state. However, the evidence in neither case is sufficient to support the causal conclusion.For instance, violent crime in general fell in the United States in the period from the mid-1980s to the present, andfor all that we can tell from the anti-gun control argumentit may have fallen at the same or higher rates in states that did not pass "right-to-carry" laws. Since the argument does not supply us with figures for the states without such laws, we cannot do the comparison.Similarly, the pro-gun control argument does not make it clear when Massachusett's drop in crime occurred, except that it was "after""post hoc"the handgun control law was passed. Also, comparative evidence of crime rates over the same period in states that did not pass such a law is missing. The very fact that comparative information isnotsupplied in each argument is suspicious, since it suggests that it would have weakened the case.Another point raised by these examples is the use of misleadingly precise numbers, specifically, "7.65%" and "5.2%" in the anti-gun control example. Especially in social science studies, percentage precision to the second decimal place is meaningless, since it is well within the margin of error on such measurements. It is a typical tactic of pseudo-scientific argumentation to use overly-precise numbers in an attempt to impress and intimidate the audience. A real scientist would not use such bogus numbers, which casts doubt upon the status of the source in the example. The pro-gun control argument, to its credit, does not commit this fallacy. This suggests, though it doesn't nail down, an appeal to misleading authority in the anti-gun control one

Other examples The rooster crows before sunrise, therefore the crowing rooster causes thesunto rise. Thedrunkscientistconducts anexperimentto see why he gets hangovers. He decides to keep a diary. Monday night, scotch and soda; Tuesday morning, hangover. Tuesday night, gin and soda; Wednesday morning, hangover. Wednesday night: vodka and soda; Thursday morning, hangover. Thursday night, rum and soda; Friday morning, hangover. On Friday night before going out for a drink, the drunk scientist has an epiphany. "Aha!" he says to himself, "I've got it! Soda causes hangovers!" In the immortal words ofAndrew Schlafly: "InRomania, abortion was illegal under two decades of rule by thecommunistdictatorNicolae Ceausescu, and the country enjoyed one of the lowest breast cancer rates in the entire world during that time, far lower than comparableWesterncountries."[3](Just because the breastcancerrate went down does not mean that the illegality ofabortionscaused it.)