The Baloney Detection Kit
by Carl Sagan
In science we may start with experimental results, data, observations,
measurements, 'facts'. We invent, if we can, a rich array of possible
explanations and systematically confront each explanation with the facts.
In the course of their training, scientists are equipped with a baloney
detection kit. The kit is brought out as a matter of course whenever new
ideas are offered for consideration. If the new idea survives examination
by the tools in our kit, we grant it warm, although tentative,
acceptance. If you're so inclined, if you don't want to buy baloney even
when it's reassuring to do so, there are precautions that can be taken;
there's a tried-and-true, consumer-tested method.
What is in the kit? Tools for skeptical thinking.
What skeptical thinking boils down to is the means to construct, and to understand,
a reasoned argument and, especially important, to recognize a fallacious or
fraudulent argument. The question is not whether we like the conclusion
that emerges out of a train of reasoning, but whether the conclusion that
emerges out of a train follows from the premise of starting point and whether
that premise is true.
Among the tools:
- Wherever possible there
must be independent confirmation of the "facts".
- Encourage substantive
debate on the evidence by knowledgeable proponents of all points of view.
- Arguments from authority
carry little weight -- "authorities" have made mistakes in the
past. They will do so again in the future. Perhaps a better way to
say it is that in science there are no authorities; at most, there are
- Spin more than one
hypothesis. If there's something to be explained, think of all the
different ways in which it could be explained. Then think of tests by
which you might systematically disprove each of the alternatives. What
survives, the hypothesis that resists disproof in this Darwinian selection
among "multiple working hypotheses," has a much better chance of
being the right answer than if you had simply run with the first idea that
caught your fancy.
- Try not to get overly
attached to a hypothesis just because it's yours. It's only a way station
in the pursuit of knowledge. Ask yourself why you like the idea.
Compare it fairly with the alternatives. See if you can find reasons for
rejecting it. If you don't, others will.
- Quantify. If whatever it is
you're explaining has some measure, some numerical quantity attached to
it, you'll be much better able to discriminate among competing hypotheses.
What is vague and qualitative is open to many explanations. Of course
there are the truths to be sought in the many qualitative issues we are
obliged to confront, but finding them is more challenging.
- If there's a chain of
argument, every link in the chain must work (including the premise) -- not
just most of them.
- Occam's Razor. This
convenient rule-of-thumb urges us when faced with two hypotheses that
explain the data equally well to choose the simpler. [simpler = the
conclusion which relies on the least number of unsupported propositions]
- Always ask whether the
hypothesis can be, at least in principle, falsified. Propositions that are
untestable, unfalsifiable are not worth much. Consider the grand idea that
our Universe and everything in it is just an elementary particle -- an
electron, say -- in a much bigger Cosmos. But if we can never acquire
information from outside our Universe, is not the idea incapable of
disproof? You must be able to check assertions out. Inveterate skeptics
must be given the chance to follow your reasoning, to duplicate your
experiments and see if they get the same result.
The reliance on carefully designed and controlled
experiments is key, as I tried to stress earlier. We will not learn much from
mere contemplation. It is tempting to rest content with the first
candidate explanation we can think of One is much better than none. But
what happens if we can invent several? How do we decide among them?
We don't. We let experiment do it. Francis Bacon provided the
"Argumentation cannot suffice for the discovery
of new work, since the subtlety of Nature is greater
many times than the
subtlety of argument."
Control experiments are essential. If, for example, a
new medicine is alleged to cure a disease 2o percent of the time, we must make
sure that a control population, taking a dummy sugar pill which as far as the
subjects know might be the new drug, does not also experience spontaneous
remission of the disease 20 percent of the time.
Variables must be separated. Suppose you're seasick. and given both an
acupressure bracelet and 50 milligrams of meclizine. You find the unpleasantness
vanishes. What did it- the bracelet or the pill? You can tell only
if you take the one without the other, next time you're seasick. Now
imagine that you're not so dedicated to science as to be willing to be
seasick. Then you won't separate the variables. You'll take both
remedies again. You've achieved the desired practical result; further
knowledge, you might say, is not worth the discomfort of attaining it.
Often the experiment must be done "double-blind", so that those
hoping for a certain finding are not in the potentially compromising position
of evaluating the results. In testing a new medicine, for example, you
might want the physicians who determine which patients' symptoms are relieved
not to know which patients have been given the new drug. The knowledge
might influence their decision, even if only unconsciously. Instead the list of
those who experienced remission of symptoms can be compared with the list of
those who got the new drug, each independently ascertained. Then you can determine
what correlation exists. Or in conducting a police lineup or photo
identification, the officer in charge should not know who the prime suspect is,
so as not consciously or unconsciously to influence the witness.
In addition to teaching us what to do when evaluating a claim to knowledge,
any good baloney detection kit must also teach us what not to do. It
helps us recognize the most common and perilous fallacies of logic and
rhetoric. Many good examples can be found in religion and politics, because
their practitioners are so often obliged to justify two contradictory
propositions. Among these fallacies are:
- Ad hominem --
Latin for "to the man," attacking the arguer and not the
argument (e.g. The Reverend Dr. Smith is a known Biblical fundamentalist,
so her objections to evolution need not be taken seriously).
- Argument from authority
(e.g., President Richard Nixon should be re-elected because he has a
secret plan to end the war in Southeast Asia -- but because it was
secret, there was no way for the electorate to evaluate it on its merits;
the argument amounted to trusting him because he was President; a mistake,
as it turned out).
- Argument from adverse
consequences (e.g., a God meting out punishment and reward must
exist, because if He didn't, society would be much more lawless and
dangerous – perhaps even ungovernable. Or: the defendant in a
widely publicized murder trial must be found guilty; otherwise, it will be
an encouragement for other men to murder their wives).
- Appeal to ignorance
-- the claim that whatever has not been proved false must be true, and
vice versa (e.g., there is no compelling evidence that UFOs are not
visiting the Earth; therefore UFOs exist -- and there is intelligent life
elsewhere in the Universe. Or: there may be seventy kazillion
other worlds, but not one is known to have the moral advancement of the
Earth, so we're still central to the Universe.) This impatience
with ambiguity can be criticized in the phrase: absence of evidence is not
evidence of absence.
- Special pleading,
often to rescue a proposition in deep rhetorical trouble (e.g., how can
a merciful God condemn future generations to torment because, against
orders, one woman induced one man to eat an apple? Special plead:
you don't understand the subtle Doctrine of Free Will. Or: how
can there be an equally godlike Father, Son, and Holy Ghost in the same
Person? Special plead: you don't understand the Divine
Mystery of the Trinity. Or: How could God permit the
followers of Judaism, Christianity, and Islam -- each in their own way
enjoined to heroic measures of loving kindness and compassion -- to have
perpetrated so much cruelty for so long? Special plead: you don't
understand Free Will again. And anyway, God moves in mysterious ways).
- Begging the question,
also called assuming the answer (e.g., we must institute the death
penalty to discourage violent crime. But does the violent crime
rate in fact fall when the death penalty is imposed? Or: the
stock market fell yesterday because of a technical adjustment and
profit-taking by investors -- but is there any independent evidence
for the causal role of "adjustment" and profit-taking; have we
learned anything at all from this purported explanation?).
- Observational selection,
also called the enumeration of favorable circumstances, or as the
philosopher Francis Bacon described it, counting the hits and forgetting
the misses (footnote)
(e.g., a state boasts of the Presidents it has produced, but is silent
on its serial killers).
- Statistics of small
numbers -- a close relative of observational selection (e.g., "they
say 1 out of every 5 people is Chinese. How is this possible? I know
hundreds of people, and none of them is Chinese. Yours truly."
Or: "I've thrown three sevens in a row. Tonight I can't lose.")
- Misunderstanding of the
nature of statistics (e.g., President Dwight Eisenhower expressing
astonishment and alarm on discovering that fully half of all Americans
have below average intelligence!).
- Inconsistency (e.g., prudently
plan for the worst of which a potential military adversary is capable, but
thriftily ignore scientific projections on environmental dangers because
they're not "proved". Or: attribute the declining
life expectancy in the former Soviet Union to the failures of communism
many years ago, but never attribute the high infant mortality rate in the
United States (now highest of the major industrial nations) to the
failures of capitalism. Or: Consider it reasonable for the
Universe to continue to exist forever into the future, but judge absurd
the possibility that it has infinite duration into the past).
- Non sequitur -- Latin
for "It doesn't follow" (e.g., our nation will prevail
because God is great. But nearly every nation pretends this to be
true; the Germans formulation was "Gott mit uns"). Often
those falling into the non sequitur fallacy have simply failed to
recognize alternative possibilities.
- Post hoc, ergo propter
hoc -- Latin for "It happened after, so it was caused by"
(e.g., Jaime Cardinal Sin, Archbishop of Manila: "I know of ... a
26-year old who looks 60 because she takes [contraceptive] pills."
Or: before women got the vote, there were no nuclear weapons).
- Meaningless question
(e.g., What happens when an irresistible force meets an immovable object?
But if there is such a thing as an irresistible force there can be no
immovable objects, and vice versa).
- Excluded middle, or
false dichotomy -- considering only the two extremes in a coontinuum
of intermediate possibilities (e.g., "sure, take her side; my
husband's perfect; I'm always wrong." Or: "either
you love your country or you hate it." Or: "if
you're not part of the solution, you're part of the problem").
- Short-term vs. long-term
-- a subset of the excluding middle, but so important I've pulled it out
for special attention (e.g., we can't afford programs to feed
malnourished children and educate pre-school kids. We need to urgently
deal with crime on the streets. Or: why explore space or pursue
fundamental science when we have so huge a budget deficit?).
- Slippery slope,
related to excluded middle (e.g., if we allow abortion in the first
week of pregnancy, it will be impossible to
prevent the killing of a full-term infant. Or, conversely: if
the state prohibits abortion even in the ninth month, it will soon be
telling us what to do with our bodies around the time of conception).
- Confusion of correlation
and causation (e.g., a survey shows that more college graduates are
homosexual than those with lesser education; therefore education makes
people gay. Or: Andean earthquakes are correlated with
closest approaches of the planet Uranus; therefore -- despite the absence
of any such correlation for the nearer, more massive planet Jupiter -- the
latter causes the former).
- Straw man --
caricaturing a position to make it easier to attack (e.g., scientists
suppose that living things simply fell together by chance -- a
formulation that willfully ignores the central Darwinian insight, that
Nature ratchets up by saving what works and discarding what doesn't.
Or -- this is also a short-term/long-term fallacy -- environmentalists
care more for snail darters and spotted owls than they do for people).
- Suppressed evidence,
or half-truths (e.g., an amazingly accurate and widely quoted
"prophecy" of the assassination attempt on President Reagan is
shown on television; but – an important detail -- was it recorded
before or after the event? Or: these government abuses demand
revolution, even if you can't make an omelette without breaking some eggs.
Yes, but is this likely to be a revolution in which far more people are
killed than under the previous regime? What does the experience of other
revolutions suggest? Are all revolutions against oppressive regimes
desirable and in the interests of the people?)
- Weasel words (e.g.,
the separation of powers of the U.S. Constitution specifies that the
United States may not conduct a war without a declaration of
Congress. On the other hand, Presidents are given control of foreign
policy and the conduct of wars, which are potentially powerful tools for
getting themselves re-elected. Presidents of either political party
may therefore be tempted to arrange wars while waving the flag and calling
the wars something else -- "police actions", "armed
incursions", "protective reaction strikes",
"pacification", "safeguarding American interests", and
a wide variety of "operations", such as "Operation Just
Cause". Euphemisms for war are one of a broad class of
reinventions of language for political purposes. Talleyrand said,
"An important art of politicians is to find new names for
institutions which under old names have become odious to the
Knowing the existence of such logical and rhetorical
fallacies rounds out our toolkit. Like all tools, the baloney detection
kit can be misused, applied out of context, or even employed as a rote
alternative to thinking. But applied judiciously, it can make all the
difference in the world-not least in evaluating our own arguments before we
present them to others.
My favorite example is this story, told about the Italian physicist Enrico
Fermi, newly arrived on American shores, enlisted in the Manhattan nuclear
weapons project, and brought face-to-face in the midst of World War Two with US
So-and-so is a great general, he was told.
"What is the definition of a great general?" Fermi characteristically
"I guess it's a general who's won many consecutive battles"
After some back and forth they settled on five.
"What fraction of American generals are great?"
After some more back and forth, they settled on a few per cent.
But imagine, Fermi rejoined, that there is no such thing as a great general,
that all armies are equally matched, and that winning a battle is purely a
matter of chance. Then the chance of winning one battle is one out of
two, or 1/2; two battles 1/4, three 1/8, four 1/16 and five consecutive battles
1/32, which is about three per cent. You would expect a few per cent
of American generals to win five consecutive battles, purely by chance.
Now has any of them won ten consecutive battles ..... ?
 Sagan, C. 1997, The Demon-Haunted World, Headline
Book Publishing, London.