post hoc fallacy - The Skeptic's Dictionary (original) (raw)
The post hoc ergo propter hoc (after this therefore because of this) fallacy is based upon the mistaken notion that simply because one thing happens after another, the first event was a cause of the second event. Post hoc reasoning is the basis for many superstitions and erroneous beliefs.
Many events follow sequential patterns without being causally related. For example, you have a cold, so you drink fluids and two weeks later your cold goes away. You have a headache so you stand on your head and six hours later your headache goes away. You put acne medication on a pimple and three weeks later the pimple goes away. You perform some task exceptionally well after forgetting to bathe, so the next time you have to perform the same task you don't bathe. A solar eclipse occurs so you beat your drums to make the gods spit back the sun. The sun returns, proving to you the efficacy of your action.
You use your dowsing stick and then you find water. You imagine heads coming up on a coin toss and heads comes up. You rub your lucky charm and what you wish for comes true. You lose your lucky charm and you strike out six times. You have a "vision" that a body is going to be found near water or in a field and later a body is found near water or in a field. You have a dream that an airplane crashes and an airplane crashes the next day or crashed the night before.
However, sequences don't establish a probability of causality any more than correlations do. Coincidences happen. Occurring after an event is not sufficient to establish that the prior event caused the later one. To establish the probability of a causal connection between two events, controls must be established to rule out other factors such as chance or some unknown causal factor. Anecdotes aren't sufficient because they rely on intuition and subjective interpretation. A controlled study is necessary to reduce the chance of error from self-deception.
Andy's story: For years I suffered a debilitating pain in my neck. I couldn't work and even the slightest activity (like brushing my teeth) was painful. My science-based medical doctor sent me to a psychiatrist who prescribed pills. They didn't do any good. I went to an acupuncturist and got some relief but it didn't last. A friend recommended the alkaline diet. At first I thought this was the answer, but again it didn't last. Another friend thought her prayer group could cure me. I went to several sessions and had hands laid all over me but to no avail. I tried aromatherapy, dolphin therapy, and therapeutic touch. Still, I suffered. I finally got relief after six years from a chiropractor. You are an idiot for criticizing chiropractors. Chiropractic was the only thing that relieved me of my pain. I am now able to work and brush my teeth with minimal pain.
Betty's story: For years I suffered a debilitating pain in my neck. I couldn't work and even the slightest activity (like brushing my teeth) was painful. My science-based medical doctor sent me to a psychiatrist who prescribed pills. They didn't do any good. I went to a chiropractor and got some relief but it didn't last. A friend recommended the alkaline diet. At first I thought this was the answer, but again it didn't last. Another friend thought her prayer group could cure me. I went to several sessions and had hands laid all over me but to no avail. I tried aromatherapy, dolphin therapy, and therapeutic touch. Still, I suffered. I finally got relief after six years from an acupuncturist. You are an idiot for criticizing acupuncture. Acupuncture was the only thing that relieved me of my pain. I am now able to work and brush my teeth with minimal pain.
Chuck's story: For years I suffered a debilitating pain in my neck. I couldn't work and even the slightest activity (like brushing my teeth) was painful. My science-based medical doctor sent me to a psychiatrist who prescribed pills. They didn't do any good. I went to a chiropractor and got some relief but it didn't last. A friend recommended the alkaline diet. At first I thought this was the answer, but again it didn't last. Another friend thought her prayer group could cure me. I went to several sessions and had hands laid all over me but to no avail. I tried acupuncture, dolphin therapy, and therapeutic touch. Still, I suffered. I finally got relief after six years from an aromatherapist. You are an idiot for criticizing aromatherapy. Aromatherapy was the only thing that relieved me of my pain. I am now able to work and brush my teeth with minimal pain.
Dora's story: For years I suffered a debilitating pain in my neck. I couldn't work and even the slightest activity (like brushing my teeth) was painful. My science-based medical doctor sent me to a psychiatrist who prescribed pills. They didn't do any good. I went to a chiropractor and got some relief but it didn't last. A friend recommended aromatherapy. At first I thought this was the answer, but again it didn't last. Another friend thought her prayer group could cure me. I went to several sessions and had hands laid all over me but to no avail. I tried acupuncture, dolphin therapy, and therapeutic touch. Still, I suffered. I finally got relief after six years from the alkaline diet. You are an idiot for criticizing the alkaline diet. The alkaline diet was the only thing that relieved me of my pain. I am now able to work and brush my teeth with minimal pain.
Edgar's story: For years I suffered a debilitating pain in my neck. I couldn't work and even the slightest activity (like brushing my teeth) was painful. My science-based medical doctor sent me to a psychiatrist who prescribed pills. They didn't do any good. I went to a chiropractor and got some relief but it didn't last. A friend recommended aromatherapy. At first I thought this was the answer, but again it didn't last. Another friend thought her prayer group could cure me. I went to several sessions and had hands laid all over me but to no avail. I tried acupuncture, dolphin therapy, and the alkaline diet. Still, I suffered. I finally got relief after six years from therapeutic touch. You are an idiot for criticizing therapeutic touch. Therapeutic touch was the only thing that relieved me of my pain. I am now able to work and brush my teeth with minimal pain.
Fiona's story: For years I suffered a debilitating pain in my neck. I couldn't work and even the slightest activity (like brushing my teeth) was painful. My science-based medical doctor sent me to a psychiatrist who prescribed pills. They didn't do any good. I went to a chiropractor and got some relief but it didn't last. A friend recommended aromatherapy. At first I thought this was the answer, but again it didn't last. Another friend thought her prayer group could cure me. I went to several sessions and had hands laid all over me but to no avail. I tried acupuncture, therapeutic touch, and the alkaline diet. Still, I suffered. I finally got relief after six years from dolphin therapy. You are an idiot for criticizing dolphin therapy. Dolphin therapy was the only thing that relieved me of my pain. I am now able to work and brush my teeth with minimal pain.
Gary's story: For years I suffered a debilitating pain in my neck. I couldn't work and even the slightest activity (like brushing my teeth) was painful. My science-based medical doctor sent me to a psychiatrist who prescribed pills. They didn't do any good. I went to a chiropractor and got some relief but it didn't last. A friend recommended aromatherapy. At first I thought this was the answer, but again it didn't last. I tried acupuncture, therapeutic touch, dolphin therapy, and the alkaline diet. Still, I suffered. I finally got relief after six years from healing prayer. A friend thought her prayer group could cure me. I went to several sessions and had hands laid all over me. Finally, I was cured. You are an idiot for criticizing healing prayer. Healing prayer was the only thing that relieved me of my pain. I am now able to work and brush my teeth with minimal pain.
Harriet's story: For years I suffered a debilitating pain in my neck. I couldn't work and even the slightest activity (like brushing my teeth) was painful. I went to my science-based doctor. She sent me to a psychiatrist who prescribed pills. I didn't take them but my pain went away a few months later and now I am unhappily back at work. My mother thinks it's a miracle, but I think the pain just went away on its own.
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See also ad hoc hypothesis, confirmation bias, control study, communal reinforcement, Occam's razor,placebo effect, regressive fallacy, selective thinking, self-deception,subjective validation, testimonials, and wishful thinking.
further reading
Giere, Ronald, Understanding Scientific Reasoning, 4th ed, (New York, Holt Rinehart, Winston: 1998).
Moore, Brooke Noel. Critical Thinking (Mayfield Publishing Company, 2000).
news
Mom: Son in 'extensive therapy' after viewing library book ... her son had removed the book unsupervised from the library’s general stacks last summer and put it in his backpack. She has kept it ever since.
“Now he’s in a home for extensive therapy,” she said.
Whoever said a little knowledge is a dangerous thing knew what she was talking about.
Desperate couple have miracle baby after acupuncture (This story is either a perfect example of post hoc reasoning or a lesson for men: we might be replaced by needles.)
Last updated 18-Nov-2015