Unintended consequences can be either

• positive, in which case we get serendipity or windfalls
• source of problems, according to the Murphy's law
• definitively negative: perverse effect, which is the opposite result to the one intended

The Law of Unintended Consequences holds that almost all human actions have at least one unintended consequence. In other words, each cause has more than one effect including unforeseen effects. The idea was originated by sociologist Robert K. Merton and is sometimes referred to as the Law of Unforeseen Consequences.

What causes this phenomenon

Much of this phenomenon is a result of the world's complexity.

Also a certain amount can be attributed partly or entirely to human stupidity, self-deception or other cognitive biases or emotional biases .

The most common kind of unintended consequences arises from perverse incentives, a term for an incentive that has the opposite effect to that intended. See the article on perverse incentives for many examples of this.

Examples of high scale unintended consequences

Of course, unintended consequences are common in everybody's life, but some can impact the whole society. Here are some examples:

• In medicine unintended consequences are known as side effects. Most drugs have some side effects. As with other unintended consequences, these are often negative, but are sometimes beneficial; for instance aspirin, a pain reliever, can also help prevent heart attacks.

• The introduction of rabbits into Australia for sport led to an explosive growth in population, and led to rabbits becoming a major pest in Australia.

• "Prohibition", intended to suppress the alcohol trade, drove many small-time alcohol suppliers out of business, consolidating the hold of large-scale organized crime over the illegal alcohol industry.

• Sixty years later, the "War on Drugs", intended to suppress the illegal drug trade, has driven many small-time drugs dealers out of business, consolidating the hold of large-scale organized crime over the illegal drugs industry.

• The medieval policy of setting up large hunting reserves for the nobility has preserved green space throughout England.

• The wartime sinking of ships in shallow waters creates artificial coral reefs.

• In CIA jargon, "blowback" describes the phenomenon of supporting a foreign regime or terrorist entity, on the principle that your enemy's enemy is your friend, only to have it attack you, often with the weapons and resources you gave it. Examples include:
  • support of Colonel Manuel Noriega
  • support of the Mujaheddin in Afghanistan, and later the Taliban
  • support of Saddam Hussein

• Numerous attempts by governments to reduce accommodation costs by the introduction of rent controls has led to the unintended consequences of shortage of property and reduction in quality or even the creation of slums — rental property not being built or maintained.

• Controversial research, carried out by John J. Donohue and Steven D. Levitt and published in the Quarterly Journal of Economics, suggests that legalized abortion accounts for as much as 50% of the drop in national crime rates. As evidence, they cite the fact that states which legalized abortion before Roe v. Wade saw drops in crime earlier, and that high-abortion states saw greater drops in crime than low-abortion states. Most convincingly, they found that, "in high abortion states, only arrests of those born after abortion legalization fall relative to low abortion states."

See also

• Side-effect
• Kludge
• moral hazard
• Murphy's law
• Perverse effects of vaccination
• Unforeseen effects of species introduction

References

• Tomislav V. Kovandzic, John Sloan III, and Lynne M. Vieraitis. Unintended Consequences of Politically Popular Sentencing Policy: The Homicide-Promoting Effects of 'Three Strikes' in U.S. Cities (1980-1999). Criminology & Public Policy, Vol 1, Issue 3, July 2002.

External references

• Atlantic magazine article: "Blowback"
• Observer article: Why 'blowback' is the hidden danger of war
• MSNBC article on Bin Laden and blowback
• Unintended Consequences