The argument from ignorance is perhaps one of the most heavily encountered when talking to people who believe in the supernatural.

It is used to support a claim by stating that the claim can't be shown to be untrue. Since this is fairly unconvincing on its own, the argument from ignorance is rarely used in isolation. Much more often it is part of a string of arguments:

'Ghosts are real because there are some scientists who believe in them / and once my windows started fogging up while I was thinking about my dead cat - so that must mean it was because of my cat's ghost, / which is more than you can say, because you can't explain to me what I saw' (can you spot what the other fallacies were?)

The reasoning behind the above line of attack is the mistaken belief that their own 'evidence,' however fallaciously it may be derived, must automatically trump the lack of evidence on the opposing side. It also, crucially, ignores the fact that if the person arguing against the claim had access to more information they would probably, indeed, be able to find a suitable explanation that didn't involve ghost cats. The fallacy gets its name because it exploits the fact that the other person is ignorant of some of the relevant data that would otherwise potentially allow for a counter-claim.

Another way that the argument from ignorance is often employed is as a last-resort tactic, where the person's usual arguments have all been successfully parried. All they can do at this point is force the other person to (correctly) agree that they do not have the evidence to disprove their claim and that there is a chance it is true. This is often an effective way of ending to make it appear that the argument/debate was more evenly matched than it really was.