An appeal to ignorance is a type of informal fallacy that arises when an argument is taken as true because it has not proven to be false, or an argument is false because it has not proven to be true.
Put differently, in an appeal to ignorance fallacy, the arguer claims that some statement P is true because someone failed to prove that P is false, or statement P is false because no one has proven that it is true. Hence, in each case, the lack of evidence or proof that P is true or false is used as a reason for concluding that P is true or false.
The form of an appeal to ignorance fallacy looks like this:
We do not know that P is false.
Therefore, P must be true.
or
We do not know that P is true.
Therefore, P must be false.
Let us consider this example to clearly illustrate this point:
Example 1
Well, I have examined all the arguments for the existence of God, and I have seen that none of them proves that God exists. That’s reason enough for me: there is no God!
In the example above, the arguer concludes that there is no God because there are no successful proofs of God’s existence. But the absence of a successful proof of God’s existence does not justify the conclusion that there is no God. What the arguer is justified in the example above is that we cannot know God.
The following examples will further illustrate the fallacy appeal to ignorance:
Example 2
The existence of heaven must be true because nobody has ever successfully defended that it is just a product of one’s imagination.
Example 3
Scientists have not proven that AIDS cannot be transmitted through casual contact. Therefore, there is no need for us to keep away from suspected AIDS carriers.