What are the "appeal to ignorance" (ad ignorantiam) and "middle ground" (false balance) fallacies?

Ad ignorantiam treats a lack of disproof as proof; false balance assumes the truth must sit halfway between two opposing positions.

• Ad Ignorantiam (appeal to ignorance) — arguing that a claim is true because it hasn't been proven false (or false because it hasn't been proven true). "Nobody has shown that ghosts don't exist, so they must." Absence of evidence isn't evidence of absence, and the burden of proof stays with whoever makes the positive claim, not with whoever doubts it.
• Middle Ground / False Balance — assuming the correct answer must be the compromise between two opposing positions. "One side says the planet is 4.5 billion years old, the other says 6,000, so the truth is probably somewhere in between." But splitting the difference is not a method for finding truth — sometimes one side is simply right, and a moderate-sounding position can be just as wrong as an extreme one.

Both swap a rhetorical position for actual reasoning: one exploits what isn't known, the other treats "moderate" as automatically "correct."

Tip: Ad ignorantiam shifts the burden of proof onto the wrong party; false balance mistakes the midpoint for the truth. Neither one actually weighs the evidence.

Go deeper:

• Argument from ignorance — Wikipedia — treating "not disproven" as "proven."
• Argument to moderation — Wikipedia — the false-balance assumption that truth sits in the middle.