The Precautionary Principle:
Common Sense or Sloppy Thinking?

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The "precautionary principle" has been proposed as a fundamental guiding principle for managing the introduction of new technology into society. The precautionary principle states that when there is some suspicion of potential danger, a lack of scientific consensus should not be used to postpone preventative or remedial action. For example, in the Cartagena Biosafety Protocol of 2000, the precautionary principle was invoked to delay the distribution of genetically-modified foods.

At first glance, the precautionary principle sounds almost reasonable--something no sensible person would oppose, like protecting the environment or using restraint in introducing potentially dangerous technologies. Indeed, some people have tried to portray the precautionary principle as a fundamental truth derived from everyday life. A few have even claimed that the precautionary principle has some basis in mathematics or statistics, giving it a glow of scientific respectability. It is also claimed that in those cases where the precautionary principle leads to clearly erroneous conclusions, it is because the principle was abused. However, in this article, I will show that it is the precautionary principle itself that is fatally flawed because it invariably biases the decision making process in favor of whichever side one wishes to take.

Few people, of course, would argue against avoiding unwarranted risks. Yet many, perhaps accustomed to the layers of protection available in contemporary welfare societies, cling to the status quo when faced with the slightest danger. The appeal of the precautionary principle is strongest among health-food advocates and environmentalists, many of whom are anxious about technology and wish to return to simpler, more "natural" times, and among anti-globalists who wish to implement radical social change to create a socialist economy based on "sustainability", zero growth, and zero-profit--a static world where the dreaded juggernaut of change can be legislated away. Hence, the precautionary principle has become highly politicized.

But even those who agree with the idea of blocking genetically modified food and preventing global increases in carbon dioxide sometimes confess to a certain undefinable uneasiness about the precautionary principle. Upon closer examination, it becomes apparent that the precautionary principle is much more than a policy of "placing the burden of proof on someone who introduces new technology". It is a superordinating premise that radically changes the way discussions of new technologies are conducted, so that rather than considering both sides impartially, one side of a dispute is placed at an almost insurmountable disadvantage. This, of course, is the purpose of the precautionary principle, and is the main reason why many environmentalists and anti-technology activists so enthusiastically promote its adoption.

However, as a guideline for public policy, this feature means the precautionary principle is fatally flawed, because it automatically leads to unwise decisions:

  1. The precautionary principle can be used to support any position or its opposite, regardless of their relative merits.
  2. The precautionary principle forces those contemplating the introduction of a technology to prove a negative, i.e., that their technology is harmless, or nearly so. Since proving a negative is impossible in principle, few attempt this. But the precautionary principle, if it were routinely applied (which it is not), would prevent all new technologies from being used, despite claims to the contrary. This would not, as some claim, be an abuse of the precautionary principle; it is the very essence of it. There is no fundamental distinction between cases where the precautionary principle leads to absurd results, like preventing the introduction of fire or the electric light, and cases where it leads to a result that saves lives. If technological advances have been implemented, it is only because the precautionary principle was not followed.
  3. The precautionary principle includes under the rubric of "new technologies" not only inventions, but also phenomena whose very existence is under question, thereby assuming that they do exist as real possibilities and are therefore a risk. In so doing, it allows arguments that would not otherwise be admitted because it is not known whether the doubts are reasonable. With the precautionary principle, any conceivable danger must be considered, whether or not it has been shown to be physically possible. Advocates of precautionary principle say that delay in waiting for evidence to decide the issue factually is unacceptable because a delay increases the damage, while acting beforehand is safer. However, this opens the door to an endless series of more and more improbable "risks" that act as barriers to new technologies.
  4. The precautionary principle ignores the risks of not introducing the new technology, which could be more severe than the risks of the technology itself. In other words, the precautionary principle is nothing more than one half of a risk-benefit analysis--the 'risk' half--and is therefore incapable of assessing the true impact of a new technology.

In this article, I will discuss several situations that have been proposed as justifications for the precautionary principle, and show that in each case, a risk-benefit analysis produces a superior result. I will also show that, contrary to what has been claimed, the precautionary principle is not commonly followed by responsible public officials, and argue that it should not be adopted as an element in decision-making.


The introduction of a new drug is a situation where prudence is warranted. In the USA, the classic case of erring on the side of caution was the denial by the Food and Drug Administration (FDA) of thalidomide, a hypnotic drug used to prevent morning sickness during pregnancy. Thalidomide was later found to be metabolized to an arene oxide that causes severe birth defects. Thalidomide can also cause nerve damage. The action by the FDA in blocking thalidomide is cited as an outstanding example of the success of the precautionary principle.

Yet, contrary to popular belief, the precautionary principle deserves no credit for blocking the clinical licensing of thalidomide in the U.S. Rather, thalidomide, along with many other drugs under consideration at the time, was blocked by bureaucratic delays. Under the Food, Drug and Cosmetic Act of 1938, drug firms were required to submit New Drug Applications (NDAs) before introducing pharmaceuticals. In those days, NDAs were automatically approved after 60 days unless the FDA determined that they did not establish the drug's safety.

Because of a record number of new drugs in the late 1950s, approval of the NDA for thalidomide was delayed by an overworked FDA reviewer in 1960 who was still studying the reports of thalidomide's neurotoxicity when researchers discovered its teratogenic effect. Only after this incident were the FDA's powers expanded so that NDAs were automatically disapproved unless the drug could be proven "safe and effective". This has increased the average pre-authorization development time for new drugs to over 16 years. Only one out of 5,000 new drugs ever succeeds in passing these hurdles.

The introduction of a precautionary principle for drugs has led to delays in treatment and prolonged suffering for thousands of patients. As one single example, it has been estimated that the FDA's prohibition against the cardiopump, which is used on unconscious heart attack victims, costs approximately 7,000 lives in the U.S. per year. The FDA's delays in approving tacrine have reduced the quality of life for thousands of Alzheimer's patients.

When the FDA replaces the precautionary principle with a true risk-benefit analysis, however, lives are saved. Thalidomide, for example, still has many beneficial uses. It inhibits the production of a molecule called tumor necrosis factor alpha (TNF-alpha), which is a potent stimulator of inflammation. Thalidomide's anti-inflammatory properties led to its becoming the drug of choice for erythema nodosum leprosum, one of the manifestations of leprosy, and it is today being considered by the FDA as a treatment for cachexia in patients with advanced AIDS.

The relative merits of the precautionary principle and risk-benefit analysis can be quantified. Take a condition that is fatal to 50% of its sufferers. Even if a drug or other treatment saves 75% of the people to whom it is administered, and its side effects kill the other 25%, a risk-benefit analysis would be overwhelmingly in favor of its use. On the other hand, if the only function of the drug were to increase the patient's bust size, a risk-benefit analysis would clearly contraindicate its use. Yet the precautionary principle would block the treatment in both cases, condemning 50% of one group to death and 100% of the other group to have smaller chest measurements.


Would this be a better world without radioactivity? Some people, considering the tens of thousands of nuclear bombs that have been built, and the disaster at Chernobyl, might unhesitatingly say so. But of course, radioactivity was discovered, not invented. It's a part of nature; without radioactivity, the universe could not exist. On Earth, radioactivity is an indispensable tool for medicine and medical research. The study of radioactivity has led to phenomenal insights into the structure of matter that have led to semiconductors and computers, and someday may tell us how the universe came into being.

As for nuclear bombs, it is no coincidence that there has not been a single large-scale war since the nuclear bomb was invented in 1945. This is not to say that nuclear weapons are a force for good. But only the most simplistic analysis would ignore the historical facts that caused nuclear weapons to be created. Unfortunately, there's a lot of simplistic analysis out there.

Would the precautionary principle have prevented nuclear technology from being introduced? Probably. If so, it would also have prevented fire technology, which despite having been instrumental in creating our technological world, has killed millions of people over the years.

Environmentalists say that "radioactivity is dangerous because it can't be contained forever". In the case of radioactivity, "forever" can be defined as a particular number of half-lives, say ten for the sake of argument. In the case of strontium-90, cesium-137, krypton-85, and europium-154, the four predominant long-lived hazardous fission products from nuclear power reactors, this would be 285, 300, 107.2, and 88 years, respectively. After 100 years, the aggregate radioactivity of nuclear waste has decayed to 1/1,000 of the levels that it had after 1 year of storage. After 1000 years, it has decayed to 1/100,000 of the 1-year levels, or about two to three million times lower than its initial level inside the reactor. So it would be prudent to store it for a thousand years or so.

If someone tells you something can't be stored, even for a thousand years, they are either being dishonest or they are unfamiliar with technology. It's just that the costs rise with the storage time. With enough effort, radioactive waste could be stored for as long as desired. It could be vitrified in microscopic particles, launched into space, or even buried under the earth's crust. The reason this is not done is that the benefits of doing so do not outweigh the costs. Suppose it is buried in a geologically stable area. Can an engineer guarantee it will remain 100% safe for a 1000 years? Of course not. No technical person would make such a statement. There are only probabilities, costs and benefits. Every event has a non-zero statistical probability of occurring. Even if the probability of a leak is lower than the probability that Ted Kennedy will spontaneously change into an enormous black hole and swallow up the universe, it is still a finite, non-zero possibility. But the precautionary principle, which considers only the costs, is inadequate for arriving at an optimal solution.


One statistician has even argued that, because a prosecutor is supposed to prove beyond a reasonable doubt the guilt of the suspect, that this is an example of the precautionary principle. Yet legal scholars would be foolish to consider merely the risks of making a mistake, as the precautionary principle would require them to do. If they did, they would never prosecute anyone, because the only way to ensure that one never convicts an innocent person is to never bring anyone to trial.

Indeed, the Founding Fathers and those in the court system who dedicate their lives to interpreting our Constitution are acutely aware of the risks and benefits of doing too little as well as doing too much. The dividing line set by the standard of proof has meandered left and right within American society as social values change over time and people reassess the relative risks of having more criminals free or more innocent persons convicted.

The precautionary principle, if it were applied to criminal law, would do much more than place the burden of proof on the prosecutor. Contrary to what its advocates claim, the precautionary principle does not say "err on the side of caution." It says, to coin a phrase, "if there is any doubt, you must throw it out". This would force the prosecutor to prove beyond any doubt that the person is guilty. Needless to say, our courts do not recognize this standard of proof. In criminal cases, the standard is "beyond a reasonable doubt". In civil cases, the standard is "preponderance of the evidence".

The key word is "evidence". The precautionary principle does not require any evidence whatsoever. If it were applied to criminal law, the defendant could say, "Your honor, there is a possibility that I may be innocent!" and the judge would have to release him.

Clearly, the precautionary principle is not applicable to criminal law. Bang. Next case.


The case of GM foods is one where there is clearly innovation, and hence one might suspect that the precautionary principle, if it can be saved, would be applicable here. The Europeans have been much criticized for their fear of GM foods, which has already resulted the starvation and death of many Africans. The reluctance of others to use "golden rice", which has been genetically modified to produce the provitamin beta-carotene, has condemned more people in the third world to blindness. Those opposed to GM foods say that in the long run, fewer people will starve if GM foods are banned, because GM foods might harm the environment.

The possibility of environmental damage is a legitimate question to ask, just as legitimate questions were raised many years ago when DNA technology was first invented. In those days, people unfamiliar with biology (which includes most environmental activists) pressed for a moratorium on DNA technology on the grounds that mutant DNA molecules might escape from laboratories and turn ordinary bacteria into lethal monster germs. That didn't happen, of course. This earlier question was quickly resolved, not by banning the technology, but by reason and evidence. And anyone who thinks DNA technology hasn't led to new wonder drugs and medical and scientific advances just hasn't been paying attention. Both the benefits and risks were considered. So it should be with genetically-modified foods.


Global warming is, of course, the raison d'être of the precautionary principle. Carbon dioxide is considered a "pollutant" by environmentalists because of the belief that it may contribute to global warming. The question of whether anthropogenic carbon dioxide contributes significantly to global warming is highly controversial. I will not discuss the scientific merits of this question here (see my article on this subject for a thorough discussion). Here I will only discuss the attempts by environmentalists and NGOs to use the precautionary principle to justify imposing limits on CO2 emissions.

Most knowledgeable parties agree that anthropogenic global warming at levels sufficient to cause environmental concern has not been proven scientifically. Hence, the environmental lobby has invented the precautionary principle to justify action in the absence of conclusive evidence.

These advocates say that delay in waiting for evidence to decide the issue factually is unacceptable because a delay increases the risk, while acting (or banning as the case may be) beforehand is safer. This sounds reasonable until one considers the even greater risks of rash action or banning a technology, in the absence of factual knowledge. Acting without considering both the benefits and the risks, in the case of global warming, means that societies will incur staggering economic losses in possibly futile attempts to protect against environmental damage whose existence can only be speculated about. The stakes are enormous. To act without knowing the facts would be irresponsible.

The issue is complicated by conflicts of interests on both sides. The Kyoto treaty appeals to the environmental lobby because it fits their socialist agenda of redistribution of wealth to poor countries. The apparent earlier success in banning chlorinated fluorocarbons (CFCs), which had been postulated to damage the ozone layer, was due not to environmentalists, but to the discovery by Dow Chemical that it could make enormous profits by substituting CFCs with new, patented chemicals. This is not to imply, of course, that there is anything wrong with making enormous profits. But it short-circuited the debate, and now some scientists are expressing doubts about the extent of the original danger.

It is often said that the risk of "doing something new" is automatically greater than the risk of maintaining the status quo. Yet in the case of CO2, the precautionary principle is turned on its head. In fact, it is the anti-CO2 NGOs that want to "do something new", namely force industrial countries to abandon fossil fuels. After all, most of this carbon dioxide was originally in the atmosphere before it was incorporated by plants into what are now fossil fuels. So, according to the precautionary principle, it never should have been allowed to turn into coal and oil in the first place. We're just restoring the original balance by returning it back where it belongs!

However, the real flaw in the supposed basis for concern about global warming in the precautionary principle is point #3 mentioned earlier: the very existence and reasonableness of the risk has not been established. How does one balance the measurable cost of reducing carbon dioxide emissions against the unmeasurable risk of not doing so, when what has not been established is not the extent of the environmental damage, but the question of whether the worries about global warming are even warranted? After all, it has been estimated that 95% of the current "greenhouse" warming, estimated at +33 degrees Celsius, is caused not by carbon dioxide but by water vapor. Is the small increment in Earth's energy balance caused by raising the absorptivity in the carbon dioxide absorption bands from 99.5% to 99.7% of incident and retransmitted radiation even a reasonable thing to worry about? How's about finding the answer before trashing the global economy? After all, that's what the precautionary principle says to do.


The environmentalist and anti-globalism activist Peter T. Saunders, who vigorously defends the precautionary principle, defined the "Anti-Precautionary Principle" as

"When a new technology is being proposed, it must be permitted unless it can be shown beyond reasonable doubt that it is dangerous. The burden of proof is not on the innovator; it is on the rest of us. The most enthusiastic supporter of the anti-precautionary principle is the World Trade Organisation (WTO), the international body whose task it is to prevent countries from setting up artificial barriers to trade. A country that wants to restrict or prohibit imports on grounds of safety has to provide definitive proof of hazard, or else be accused of erecting false barriers to free trade. A recent example is WTO's judgment that the EU ban on US growth-hormone injected beef is illegal."
In fact, the real reason the WTO ruled against the ban was that the EU had pressed for a permanent ban, rather than a temporary one that could have held off beef imports until more scientific evidence could be accumulated. Thus, the European position had little to do with any precautionary principle. It was a protectionist gambit that properly failed.

In this, Saunders also makes a very common logical error: he supposes that there exist people who believe in the opposite of his thesis, namely his so-called "anti-precautionary principle". However, as shown here, the precautionary principle is quite meaningless, and therefore so is its opposite. It is a false dichotomy.

Consider, however, the argument of the anti-globalism activists who argue that definitive proof of safety should be required, as a precautionary measure. This extreme interpretation illustrates the untenability of the precautionary principle, which turns the scientific process on its head.

Should a country exporting beef from animals injected with growth hormone bear the burden of proof that no detectable hazard exists? Superficially, it might sound reasonable. Surely, they should have to test it for hazards. But how would they prove there is no hazard, especially in the face of protectionists who invoke the precautionary principle to insist that "no demonstrable hazard" is not good enough? Indeed, it is a fundamental axiom of science that proving a negative is impossible, not just in practice, but in theory.

Believers in the precautionary principle might say that when someone requires proving a negative, that person is abusing the precautionary principle. This is not so. It is the precautionary principle itself that requires proving the negative. If there is a possibility of permanent harm, the technology must be abandoned. There is only one interpretation of this: to be accepted, there must be no possibility of permanent harm. To claim the precautionary principle doesn't state this would be tantamount to invoking the precautionary principle only in cases where one is confident it won't lead to a logical inconsistency. Such an approach would be intellectually dishonest.

As an example, suppose you wanted to prove, for some unfathomable reason, that it never rained on the moon. It sounds like a sure bet. But how would you prove it? If you look at the moon and find no puddles of water, someone could say "they could have evaporated". If you set up rain gauges that measure zero every year for a thousand years, someone could always say "it could rain every 1001 years". There is simply no way to prove that it doesn't rain on the moon, because it is a negative. Conversely, all one would have to do to prove that it does rain on the moon would be to find a single raindrop.

Thus, Saunders' argument against the WTO is pure beef puckey. More to the point, it is, if anything, a clear example where the "precautionary principle" simply cannot work.


It is sometimes claimed that the precautionary principle is based on sound statistical and mathematical principles, and that scientists utilize the precautionary principle, perhaps without realizing it, in the course of their work. Nothing could be farther from the truth. In fact, scientists do not follow the precautionary principle. Nor do they follow the "anti-precautionary principle", the straw man argument that Saunders posits as its alternative.

Let's review what the precautionary principle says: if there is risk of permanent harm, the new policy should not be implemented. Applied to knowledge, the principle would be: if there is a possibility of being wrong, the conclusion should not be accepted.

At first glance, it may appear that scientists, who give the appearance in their writings and statements of being conservative and cautious, are following this principle of absolute risk-aversion. But they aren't. When a scientist rejects a new hypothesis, the reason is not that it might be wrong. A good scientist rejects a hypothesis only if it is inconsistent with the evidence, in which case it is definitely wrong. If there is not enough evidence, a scientist will simply say that the evidence is insufficient. The hypothesis is not accepted, but it's not rejected either. The reason it's not accepted is that it can't be. It's how modern science works.

So far, at least to a layperson, the difference between this and the precautionary principle may be subtle. But the key difference is this: a scientist will also not reject a hypothesis without evidence. This is not because the burden of proof has somehow shifted, or that the precautionary principle does not apply for the case of rejecting hypotheses. It is simply that the scientist is not following the precautionary principle at all. The scientist is following the principle that every conclusion must be derivable from repeatable observations. In this context, prematurely rejecting a hypothesis in the face of inadequate evidence, as the precautionary principle would dictate, would be equally bad science as prematurely accepting it.

Of course, there are bad scientists out there who reject good hypotheses or accept bad ones for the wrong reason. I've worked with a few of them. But they weren't supposed to do it. Not because it's wrong, but because you wouldn't discover much if you followed the precautionary principle instead of empirical logic.

This is the mechanism by which science moves forward. Hypotheses are salvaged and recast into new hypotheses that better fit the observations. If the evidence is insufficient, the hypothesis isn't rejected; it evolves and becomes the subject of a bigger and costlier grant application. Neither the precautionary principle nor risk-benefit analyses apply to the way a scientist conducts research.

That's a lucky break for global warming advocates. If the precautionary principle did apply to science, it would dictate that the global warming hypothesis should be rejected because there are doubts about its validity. Of course, as mentioned above, the precautionary principle can be used to justify either side of any argument. It can just as easily reject the hypothesis that global warming is not occurring. Guess which interpretation the environmentalists pick.


Similarly, when researchers looked for a link between extremely low frequency (ELF) radiation emitted from power lines and cancer, it would have been inconceivable for them to test the hypothesis that "ELF radiation is not harmful". Instead, they looked for a positive correlation. They found nothing. But does this prove that ELF electromagnetic radiation does not cause cancer? No. This is unprovable. It is even possible that ELF causes some unknown, unexpected, and unmeasurable harm, such as preventing humans from having extrasensory perception or preventing their soul from escaping after death. Thus, one could invoke the precautionary principle to prevent construction of power lines on this basis. With the precautionary principle, facts and evidence are not needed; the mere possibility of potential harm would be enough to invoke the precautionary principle to prevent the introduction of electricity. The precautionary principle imposes an impossible burden on the developers of some new technology by forcing them to prove that it is absolutely safe. And many people have died because of electricity. Yet we still use it. The same with fire.

Indeed, if the precautionary principle were a valid reasoning tool, it would stop not just electricity and fire, but all innovation. It could be used to justify any action or its opposite. Stated another way, the precautionary principle is "If there is a risk, even if it is unproven, unprovable, or even a mere fantasy in the minds of opponents of the action, then the action should not be taken." The real problem with the precautionary principle is that it does not require facts, evidence, or rational evaluation of benefits vs. risks. That's why NGOs and environmentalists like it. Ignoring one risk and emphasizing another to justify one's pre-established point of view is simple intellectual dishonesty. And that's what the precautionary principle is really all about.