Taxonomy: Logical Fallacy > Informal Fallacy > One-sidedness7

Subfallacy: Quoting Out of Context


He who knows only his own side of the case, knows little of that. His reasons may be good, and no one may have been able to refute them. But if he is equally unable to refute the reasons on the opposite side; if he does not so much as know what they are, he has no ground for preferring either opinion.8



You've spoke about having seen the children's prisons in Iraq. Can you describe what you saw there?

The prison in question is at the General Security Services headquarters, which was inspected by my team in Jan. 1998. It appeared to be a prison for children—toddlers up to pre-adolescents—whose only crime was to be the offspring of those who have spoken out politically against the regime of Saddam Hussein. It was a horrific scene. Actually I'm not going to describe what I saw there because what I saw was so horrible that it can be used by those who would want to promote war with Iraq, and right now I'm waging peace.9


A one-sided argument presents only evidence favoring its conclusion, and ignores or downplays the evidence against it. One-sidedness is a fallacy of inductive, rather than deductive, reasoning. In induction there is a Total Evidence Requirement10, which means that one must consider all of the available evidence before coming to a conclusion. For example, suppose that you have observed several white swans; then you might reason inductively to the conclusion:

All swans are white.

However, if you have observed even one black swan, you should not come to this conclusion. Instead, you might draw one of the weaker conclusions: Escher swans detail

So, the total evidence available to you consists in observations of several white swans and a black one. Whatever conclusion that you draw needs to be consistent with this evidence, but "all swans are white" is inconsistent with there being even one black swan. To leave the black swan out would be an instance of the fallacy of One-sidedness.


It is by no means always fallacious to present a one-sided argument. As is usual with fallacies, we have to take the context of the argument into consideration. For instance, a trial attorney presents a one-sided case in favor of a client. It is not a defense attorney's job to present the evidence for the defendant's guilt, rather that is the job of the prosecutor. Likewise, the prosecutor's job is to present a one-sided case for conviction. Both sides are presented in a trial, just not by the same persons. This is the way that adversarial systems, such as the legal system, work: each side presents a biased case, and the jury comes to a decision based upon hearing both sides. In this way, even though each side is one-sided, all of the relevant evidence is presented by whichever side it happens to favor.

Other contexts of argumentation are similarly adversarial, for example, partisan politics such as election campaigns. A candidate's campaign will present only a positive case for the candidate's election, and a case against the candidate's opponents. However, the other side can always be relied upon to present the negative case. We voters, by listening to both sides of the campaign, can make an objective decision about how to vote based upon all the available evidence. This is why it is important to pay attention to all sides during a campaign, and to hear different political points of view. People who listen to only one side will inevitably form one-sided opinions.

Another major source of non-fallacious bias is in the world of advertising. We have no reason to expect advertisers or salespeople to tell us what is wrong with their product, or why we should buy some other manufacturer's product instead. This is why we should take such pitches with a heavy dose of skepticism. Unfortunately, all too seldom do we hear the other side of the argument, as promoters of products seem to be reluctant to criticize competitors. As rational consumers, we need to turn to consumer publications to hear the other side of the story.


One-sidedness is fallacious in contexts where we have a right to demand objectivity. Two such contexts are news stories and scientific or other scholarly writing:

Reader Response:

It seems to me there are many kinds of one-sidedness that are strategies more than arguments. For example, what I call "controlling the microphone." If somehow one side can control when a microphone is turned on (literally or figuratively), then the opposition may not be heard. If one side controls access to mass media, to certain publications, etc., then only their side is presented or their opponents' arguments are filtered to their advantage. Congress has variants of this, for example, "filling up the amendment tree" which prevents opposing amendments from being added. Or simply limiting debate before all the issues have been aired. The judicial branch may deny someone a hearing which lets the status quo stand without further argument. Large advertisers try to fill the airwaves with their pitch, leaving little space for the opposition. I'm tempted to call these something like meta-fallacies or hyper-fallacies because they aren't arguments per se but strategies for promoting something.―Ralph Gillmann

I would resist the temptation if I were you. A "meta-fallacy" would be a fallacy about a fallacy, and a "hyper-fallacy" would be a fallacy on steroids, neither of which seems right. The examples that you give are all good examples of what I call "boobytraps", that is, nonarguments that can cause someone to fall into fallacious reasoning. Much of what is called "slanting", or―in the context of propaganda―"card stacking", is the setting up of one-sided boobytraps.

Slanting can be one of the most insidiously deceptive boobytraps, because simply leaving out relevant information can lead people seriously astray. In order to do this, dictatorships and totalitarian governments have always attempted to monopolize the news media and education, in order to control what information people receive. It's almost impossible to detect such one-sidedness if you lack other sources for the relevant facts, which is what makes a free press so important.


  1. This term seems to have originated with the Institute for Propaganda Analysis, a short-lived think tank that started in the late-1930s and closed down when the United States entered World War 2. As part of its public education efforts, it created a list of seven propaganda devices, one of which was "card stacking". See: Alfred McClung Lee & Elizabeth Briant Lee, editors, The Fine Art of Propaganda (1939), Chapter 9.
  2. "Cherry picking" usually refers to one-sidedness in the selection or presentation of numerical or statistical evidence, that is, one picks only the numbers or statistics―the "cherries"―that support a conclusion and ignore those that do not. See: Joel Best, More Damned Lies and Statistics (2004), pp. 157-8 and Charles Seife, Proofiness (2010), pp. 26-7. Thanks to Gary Herstein for asking about cherry picking.
  3. T. Edward Damer, Attacking Faulty Reasoning: A Practical Guide to Fallacy-Free Arguments (Third Edition) (Wadsworth, 1995), pp. 147-149.
  4. Madsen Pirie, How to Win Every Argument: The Use and Abuse of Logic (2013).
  5. Monroe C. Beardsley, Thinking Straight: Principles of Reasoning for Readers and Writers (Prentice-Hall, 1950), Section 14. "Slanting" is the term for one-sidedness most often used in the context of journalism or history. "Slanting" may also refer to a very different phenomenon, namely, the use of emotive language in order to influence an audience towards a particular evaluation. Thanks to Mary and Marvin for asking about slanting.
  6. R. T. Carroll, "Fallacy of Suppressed Evidence", The Skeptic's Dictionary, 10/27/2015.
  7. Peter Suber, "The One-Sidedness Fallacy". A handout for a logic course.
  8. John Stuart Mill, On Liberty.
  9. Massimo Calabresi, "Scott Ritter in His Own Words", Time, 9/14/2002.
  10. A. R. Lacey, "Confirmation", A Dictionary of Philosophy (3rd Revised Edition, 1996).