Tips On Arguing: Argument from Ignorance

Inquiry:

In Latin (and formal logic), this is known as the “argumentum ad ignorantiam.” There are two basic types, both founded on a lack of evidence.

The first says that because there is not enough evidence to prove something, it can’t be true. The obvious mistake here lies in the assumption that no further evidence will ever be found.

There is a perfect example of this in ancient Greek philosophy, when the philosopher Democritus speculated that all matter was made up of pieces floating in space that were all basically the same, but fit together in different ways to make up everything in the world. This view lost prominence for many centuries, because few could imagine things like water and fire being composed of the same materials. But by 1808, enough scientific research had been done for chemist and physicist John Dalton to put forth the first atomic theory (the word “atom” came directly from Democritus’ ideas).

The lesson? You can never say that something is impossible – just unlikely.

The other type of argument from ignorance states that because there is not enough evidence to prove one hypothesis, another hypothesis is automatically true.

This form of argumentum ad ignorantiam has led to some of America’s darkest moments. In the 1950’s, Joseph McCarthy began accusing many high-profile citizens as being communist sympathizers or spies.

In his 1995 book, Arguments from Ignorance, University of Winnipeg Philosophy Professor Douglas N. Walton explained why McCarthyism failed the litmus test of logic: “You were presumed guilty, once accused, and the burden then lay on the accused party to provide evidence of being innocent.” McCarthy sometimes openly said that his reason for making an accusation was the fact that he had no evidence to suggest that the person was not in league with the communists.

This is the reason that the argument from ignorance can be so dangerous. The fears that allowed McCarthyism to flourish overshadowed rational considerations for both the general public, as well as some government officials. As Walton notes, this kind of negligence “can be very convincing for a time, with devastating effects on affected individuals.”

The lesson? Just because there’s no evidence for one thing doesn’t necessarily mean another thing is true.