Argumentum ad Ignorantiam
(Appeal to Ignorance) Fallacy:
The Ad ignorantiam fallacy is the logical error
occurring when a proposition is unjustifiably claimed to be true simply
on the basis that it has not been proved false
the logical error occurring when a proposition is unjustifiably
claimed to be false simply because it has not been proved true.
(2) Read and analyze the following passages.
(3) Explain with a sentence or two as to whether or not you
judge an ad ignorantiam fallacy to be present.
Check your answer.
Ad Ignorantiam Example Exercises
“What happened last week to White House Press Secretary Sarah
Huckabee Sanders and her friends at the Red Hen restaurant … [was
that her] ideology led to Sanders and her party being expelled from the
establishment. A waiter had served their meal, but after learning that
Sanders was there, the owner asked her to leave. … Those who claim
to be defenders of free speech and free association have been stangely
quiet about the incident, leading one to believe they support the restaurant
Comment: The ad ignorantiam fallacy occurs. Mr. Thomas argues
that since defenders of free speech and free association have not objected to
Ms. Sanders' ouster, they must have supported the restaurant owner's decision.
“[T]o reach its secondhand smoke conclusions, the Environmental
Protection Agency employed statistical techniques that were grossly dishonest.
Some years ago, I had the opportunity to ask a Food and Drug Administration
official whether his agency would accept pharmaceutical companies using similar
statistical techniques in their drug approval procedures. He just looked at
Comment: Implicitly, there is an ad ignorantiam appeal. From
the fact that a Food and Drug Administration official does not respond to a
question, one cannot conclude the official's agreement or disagreement to the
point at issue.
”Opponents of comprehensive sex education in the state, including
Christian lobbying groups and other social conservatives, said any deviation
from an abstinence-focused curriculum will encourage risky behavior. But there
is no scientific evidence to back up that claim. In fact, a 2007 federal study
indicated abstinence-only programs had no impact on the rate of teen sexual
Comment: The argument is not an ad ignorantiam
fallacy since evidence to the contrary of the claim that abstinence-focused
curricula encourages risky behavior is provided.
“The Education Endowment Fund (EEF) even published some research
findings in 2015 showing that philosophical discussion among pupils led to
small improvements in reading and maths performance in primary schools. …
Stephen Gorard, one of the academics behind this research, said that perhaps the
best we can say from these findings is that philosophy doesn't harm Sats outcomes.
The EEF research shows, then, that there are no good reasons not to do
Comment: Since some evidence is given, the ad
ignoratiam fallacy does not occur. Instead the fallacy of
ignoratio elenchi (irrelevant
conclusion) occurs. The argument is since the EEF research shows philosophical
discussion leads to small improvement in reading and math, the EEF research
shows there are no good reasons not to do philosophy. From the fact that there
is some evidence for a conclusion, it does not logically follow that there is
no evidence against that conclusion.
“I would like to see the federal government streamlined, but Thomas
G. Donlan was being — at best — facile and premature in saying that
the federal operations were shut down ‘without being missed.’ No one
knows what harm may have been caused during the shutdown because no one has an
instant knowledge of all federal activitiess — what furloughed intelligence
analysts may have missed spotting; which Commerce Department export initiatives
were damaged; which oil-rig inspection will now prove to be two weeks late,
Comment: The ad ignorantiam fallacy occurs in the
passage. Initially, it might seem as though Mr. Machlowitz is merely making
the point that without further information we cannot conclude no harm was
done by the federal shutdown. In this he is correct, but he claims that we do
not know the harm that was done because we do not yet have knowledge
of those federal activities which will prove to be harmful. If there is no
information of harm done at the present time, then on the basis of that fact,
it is not now known whether there will be or will not be damages occurring as
a result of the shutdown without further evidence being presented.
“The wide appeal of the idea that some students will
learn better when material is presented visually and that others will learn
better when the material is presented verbally, or even in some other way, is
evident in the vast number of learning-style tests and teaching guides available
for purchase and used in schools. But does scientific research really support
the existence of different learning styles, or the hypothesis that people learn
better when taught in a way that matches their own unique style?
Unfortunately, the answer is no, according to a major new
report published this month in Psychological Science in the Public
Interest … [A]lthough numerous studies have purported to show the
existence of different kinds of learners (such as ‘auditory learners’
and ‘visual learners’), those studies have not used the type of
randomized research designs that would make their findings
Comment: No fallacy occurs. The passage describes new randomized
research on a topic that provides better evidence that older non-randomized
“Heeled footwear began to be used more than a 1000
years ago, and led to the occurrence of the first cases of schizophrenia.”
“Many data suggest an association between the use
of heeled footwear and schizophrenia and they could probably be questioned in
many instances. I have however not been able to find any contradictory data.
One possibility would be the existence of young patients not being able to use
their legs during many years and yet having schizophrenia. I have never seen
such a patient. I suggest that there is an association between the use of heeled
footwear and schizophrenia.”
Comment: The fallacy of ad ignorantiam occurs. From
the fact the author has not personally observed a patient having a certain
characteristic, it does not logically that no such patient exists.
“Statistics go to prove that good years and bad years [for the number
of herring off the Scottish coast] run in groups, and the recent series of
bad years was almost exactly paralled thirty-two years ago. [I]t has not been
proved that our seas have been depleted of food-fishes to a dangerous extent
by man … the sea can hold its own even against human
Comment: Since the author argues from the fact that it has not been
proved that the Scottish waters have been over-fished, it follows that the
oceans will continue to provide enough fish. Thus, the ad
ignorantiam fallacy occurs.
“Such a gigantic will as that of a Buddha or a Jesus could not be obtained
in one life, for we know who their fathers were. It is not known that their
fathers ever spoke a word for the good of mankind. … If it was only a
case of hereditary transmission, how do you account for this petty prince, who
was not, perhaps, obeyed by his own servants, producing this son, whom half a
world worships? How do you explain the gulf between the carpenter and his son,
whom millions of human beings worship as God? It cannot be solved by the theory
Comment: The fallacy of ad ignorantiam occurs. From
the fact that we do not know anything the fathers of Buddha and Jesus
spoke, we cannot conclude anything about their character. Also the fallacy of
complex question occurs presupposing that
necessarily there was “a gulf” between father and son. From the
fact that we can't account for something, we cannot form a definite conclusion.
“That Christ could laugh is beyond dispute, for He was a man
and risibility his proprium.
A characteristic not essential to a species, but is unique and
conventional to it. For example, human beings have the characteristic
That He did not laugh we may conclude … from
the silence of the gospels. As to why he did not, Jorge believes it
is because He recognized that laughter, proprium or not, is
inappropriate for those who server God and seek
Comment: The ad ignorantiam fallacy occurs since
the author argues that because the New Testament gospels did not record Christ's
laughter, Christ never did so.
“National Public Radio reported last month ‘the FBI has conducted
more than 100 investigations into suspected Islamic extremists within the
military.’ What else would infiltration look
Comment: From the fact that there were many investigations of
something, one cannot conclude that those investigations were successful.
Since no substantiation of the investigations was mentioned, one cannot
logically conclude that any of the investigations were successful. Some
evidence must be presented. The fallacy of ad ignorantiam
“Consumer Reports has urged the U.S.
Food and Drug Administration to develop a standard for allowable levels of arsenic
for rice, after its study found traces of the element in rice and rice product
samples it tested. It also recommends that adults and children limit their
consumption of rice and rice products
The USA Rice Federation responded quickly to the study, saying
rice's reputation as a nutritious, healthy and safe food is well-established.
‘We are aware of concerns about the level of arsenic in food, but are not
aware of any established studies directly connecting rice consumption and adverse
health effects,’ said Anne Banville, vice president, domestic promotion for
the USA Rice Federation.”
Comment: The argument is implicit that since the USA Rice Federation
is not aware of any “well-established” studies showing arsenic in
rice is harmful, rice's reputation as a safe food is sustained. Rice consumption
might be safe, but this argument does not show that it is. The fallacy of
ad ignorantiam occurs.
“Of finite sets in nature may be mentioned the totality of electrons in the
universe, or all the stars. It is supposed by at least one reputable authority that
these sets are indeed finite, but it has not been proved. That the set of all stars
is a discrete set is obvious.”
Comment: No fallacy is present since there is no argument.
Even if it were contextually an argument, it's not contradictory to suppose
that a statement can both be obvious and not proved.
“Leading air-safety experts have concluded that the captain of flight
MH370 deliberately crashed the plane. … A Canadian air-crash investigator,
Larry Vance, said he believed that Captain Zaharie put on an oxygen mask before
depressurising the plane to render the passengers and crew unconscious:
‘There is no reason not to believe that the pilot did not depressurise
the cabin to incapacitate the
Comment: Captain Zaharie is said to have depressurized the plane on
the grounds that there is no reason not to believe he didn't. The fallacy of
ad ignorantiam occurs.
“Fifth Amendment Can't Shield Selective Answers”
“A murder suspect's silence during initial questioning
by police can be used against him at trial, the sharply divided Supreme Court ruled
Monday. ‘It has long been settled that the privilege “generally is not
self-executing” and that a witness who desires its protection “must
claim it,”’ according to the lead opinion written by Justice Samuel
Alito and joined by Chief Justice John Roberts and Justice Anthony Kennedy.
Although ‘no ritualistic formula is necessary in order
to invoke the privilege … a witness does not do so by simply standing
mute,’ Alito added.
In so ruling, we explained that ‘if [the defendant]
believed that his failure to cooperate was privileged, he should have said so at
a time when the sentencing court could have determined whether his claim was
legitimate,’ the decision states.”
Comment: The court has ruled that a suspect's silence is evidence that
may be used at trial unless the suspect specifically invokes his right not to
speak. This is a ruling of the court as to legislative procedure — not an
argument. No fallacy occurs.
1. Cal Thomas, “Bigotry Returns to Virginia,”
Index-Journal 100 no. 102 (June 28, 2018),
2. Walter Williams, “Bizarre Arguments and Behavior,”
Index-Journal 95 no. 308 (March 27, 2014),
3. Editor of Herald of Rock Hill S.C. quoted in “Better
Sex Education Needed in Our Sate,” Index-Journal 94
no. 360 (April 26, 2013), 8A.↩