What fallacy is being used when someone argues that their conclusion is correct simply because it hasn't been disproven?

The fallacy being employed in this scenario is an Appeal to Ignorance. This fallacy occurs when an argument asserts that a proposition is true simply because it has not been proven false, or conversely, that it is false because it has not been proven true. This reasoning is flawed because the lack of evidence against a position does not inherently substantiate that position.

For instance, claiming that extraterrestrial life exists solely because we have not conclusively proven that it does not is a classic example of this fallacy. It shifts the burden of proof onto the other party to disprove a claim rather than requiring the claimant to offer valid evidence supporting their assertion.

In this context, it is essential to understand that beliefs or conclusions should be based on evidence and logic rather than the absence of disconfirming evidence. This understanding helps to clarify the distinction between valid argumentation and flawed reasoning.