Suppressed Evidence Fallacy

In the discussion about inductive arguments, it is explained how a cogent inductive argument had to have both good reasoning and true premises, but the fact that all included premises have to be true also means that all true premises have to be included. When true and relevant information is left out for any reason, the fallacy called Suppressed Evidence is committed.

The fallacy of Suppressed Evidence is categorized as a Fallacy of Presumption because it creates the presumption that the true premises are complete.

Examples and Discussion

Here is an example of Suppressed Evidence used by Patrick Hurley:

1. Most dogs are friendly and pose no threat to people who pet them. Therefore, it would be safe to pet the little dog that is approaching us now.

It should be possible to imagine all sorts of things which might be true and which would be highly relevant to the issue at hand. The dog might be growling and protecting its home, or it might even be foaming at the mouth, suggesting rabies.

Here is another, similar example:

2. That type of car is poorly made; a friend of mine has one, and it continually gives him trouble.

This might seem like a reasonable comment, but there are many things that might be left unsaid. For example, the friend might not take good care of the car and might not get the oil changed regularly. Or maybe the friend fancies himself as a mechanic and just does a lousy job.

Perhaps the most common use of the fallacy of Suppressed Evidence is in advertising. Most marketing campaigns will present great information about a product, but will also ignore problematic or bad information.

3. When you get digital cable, you can watch different channels on every set in the house without purchasing expensive extra equipment. But with satellite TV, you have to buy an extra piece of equipment to each set. Therefore, digital cable is a better value.

All of the above premises are true and do lead to the conclusion, but what they fail to note is the fact that if you are a single person, there is little or no need to have independent cable on more than one TV. Because this information is ignored, the above argument commits the fallacy of Suppressed Evidence.

We also sometimes see this fallacy committed in scientific research whenever someone focuses on evidence which supports their hypothesis while ignoring data which would tend to disconfirm it. This is why it is important that experiments can be replicated by others and that the information about how the experiments were conducted be released. Other researchers might catch the data which was originally ignored.

Creationism is a good place to find fallacies of Suppressed Evidence. There are quite a few cases where creationist arguments simply ignore evidence relevant to their claims, but which would cause them problems. For example, when explaining how a "Great Flood" would explain the fossil record:

4. As the water level began to rise, the more advanced creatures would move to higher ground for safety, but more primitive creatures would not do so. This is why you find less complex creatures further down in the fossil record and human fossils near the top.

All sorts of important things are ignored here, for example, the fact that marine life would have benefitted from such a flood and the would not be found layered in such a way for those reasons.

Politics is also an excellent source of this fallacy. It isn't unusual to have a politician make claims without bothering to include critical information. For example:

5. If you look at our money, you will find the words " In God We Trust." This proves that ours is a Christian Nation and that our government accepts that we are a Christian people.

What is ignored here is, among other things, that these words only became mandatory on our money during the 1950s when there was a widespread fear of communism. The fact that these words are so recent and are largely a reaction to the Soviet Union makes the conclusion about this being politically a "Christian Nation" much less plausible.

Avoiding the Fallacy

You can avoid committing the fallacy of Suppressed Evidence by being careful with regard to any research you do on a topic. If you are going to defend a proposition, you should make an attempt to find contradictory evidence and not simply evidence which supports your presupposition or beliefs. By doing this, you are more likely to avoid missing crucial data, and it is less likely that anyone can reasonably accuse you of committing this fallacy.