Argument from ignorance, or argumentum ad ignorantiam, infers that a proposition is true from the fact that it is not proven to be false (or alternatively, that a proposition is false because it is not proven to be true).
The old argument that “the absence of evidence is not evidence of absence” is a form of this logical fallacy, because absence of evidence can be evidence of absence if substantial attempts to find evidence have proven negative.
This fallacy also asserts that a proposition is true because it has not yet been proven false, or it is “generally accepted” (or vice versa).
Furthermore, this argument presumes that there are only two choices: true or false. In fact, there are other choices, including “not enough investigation has been completed to choose between true or false.” So a non-fallacious argument may be made that a proposition is not false because insufficient testing has been done to show it false. That is a reasonable argument.
Appeals to ignorance are used to shift the burden of proof to the other side. However, the burden of proof should be on the side that is making the assertion, not on the side that disputes the assertion.
There is no evidence that says a god doesn’t exist, so a god must exist.