Appeals to ignorance and the burden of proof
The basis of a an appeal to ignorance (also called argumentum ad ignoratium or argument from ignorance, see Walton) is that whatever has not been disproved must be correct. The problem with this type of argument can be seen in these two examples:
"No one has ever proved that the Loch Ness Monster exists, so it must not exist."
"No one has ever proved that the Loch Ness Monster does not exist, so it must exist."
These arguments are contradictory, only one can be true and it is not possible to tell which one it is. Such an argument proves nothing, its main effect is to shift the burden of proof. (Stated properly, an appeal to ignorance is not a fallacy. This statement is perfectly good but of course does not prove that nessie does not exist: "Numerous searches of the loch have been made and no monster has ever been found. And the "evidence" for the monster has been shown to be fake or caused by natural phenomena. We can reasonably assume that there is no Loch Ness Monster.")
More example of appeals to ignorance:
"No one has ever proved that silicon breast implants (or electromagnetic fields or whatever) are safe."
"No one has ever proved that silicon breast implants are unsafe."
Senator Joseph McCarthy (from Walton pages 3-4): "I do not have much information on this except the general statement of the agency that there is nothing in the files to disprove his Communist connections." Of course a lack of proof that someone is not a Communist is not proof that they are a communist.
"I do not know that this gun is unloaded, so I will assume that it is loaded." This is an example of the precautionary principle. In the face of a lack of knowledge it is better to be safe than sorry.
A special case is what I call an appeal to personal ignorance. In this case the author does not know of proof for (or against) an argument, and so assumes that no such proof exists. Dixy Lee Ray (with Lou Guzzo) was particularly good at making this type of argument. In Environmental Overkill (page 35) she wrote: "How does CFC rise when its molecules are four to eight times heavier than air? All experience with freon and related CFCs shows that they are non-volatile and so heavy that you can pour CFCs from a container and if some of them spill, they will collect at the lowest point on the ground where soil bacterial will decompose them. Of course, some molecules will be caught in upward air eddies or otherwise carried upwards, but this is a very small fraction of the total." She does not appear to have made any effort to answer the question in the first sentence. She did not consult with any atmospheric scientists, or check any reference work, scientific paper or government report. Instead she simply assumed that no known mechanism existed. (This claim has been debunked several times, see Parson, Rowland) Also on page 35 she wrote "We do not know how these heavier-than-air molecules cross the equatorial counter currents to accumulate at the South Pole and do the most ozone destruction there." If by "we" she meant co-author Guzzo and herself then she is probable right. But if by "we" she meant the scientific community then she is very wrong (Parson ) (and CFCs simply do not accumulate at the South Pole).
In general, it is up to the person making an argument to try to prove it. Of course, there are special cases where the burden of proof is assigned. In criminal court cases (in the United States) it is up to the prosecution to prove guilt "beyond a reasonable doubt." With chemicals and other manufactured products it was at one time up to the public to show that the products were unsafe. Over time, the burden of proof has been shifting to the manufacturers to prove safety. For example, pharmaceuticals must be proven to be safe and effective before they are permitted. Most environmentalists would like to see the burden of proof shifted to the manufacturers for all types of products (the precautionary principle).
Things to remember
In general, it is up to the person making a claim to try to prove it. Do not be tricked into trying to disprove someone else's claim.
Extraordinary claims require extraordinary proof.
Absolute certainty is not required to set public policy (in fact, there is no such thing as absolute scientific certainty). We do not have to prove that ozone depletion or global warming are real, or that the Bermuda Triangle is not real, to set public policy.
References
Parson, Robert, A critical analysis of two chapters from: Environmental Overkill.
Rowland, Sherwood, "The Need for Scientific Communication with the Public" Science, June 11, 1993, pp 1571-1576.
Walton, Douglas, Arguments from Ignorance, The Pennsylvania State University Press, 1996.
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Written by Jim Norton
Visit my practical skepticism page
Visit my anti-environmental myths home page.
The text on these pages may be freely copied, distributed and posted as long as my name, this statement and the URL (http://info-pollution.com/ignorance.htm) are included.