Now, how could we prove this theory? What would be different if it were true or false?
The correct answer is obviously “Ask your GM.” That aside, maybe you could convince a good or neutral cleric to raise undead, then Detect Evil? (Disclaimer: I have only a basic understanding of D&D mechanics, and the alignment system never made sense to me either.)
You’d probably need a neutral cleric to do that, but they’d have to be careful, since some DMs might make premediated casting of a [evil] spell simply to gain knowledge as something that would push a neutral individual over to evil.
If said cleric casts that Evil spell, but does it unknowingly (e.g. mind control, or other more convoluted scenarios, perhaps involving magical sensory deprivation), are they still considered to have done an Evil act?
Yes, though it’s usually not much of an Evil act. More to the point, in most versions, clerics are prohibited from using opposed-alignment spells, which nicely insulates them from accidental alignment shifts due to spellcasting.
A good wizard, on the other hand, can actually cast protection from good (an evil spell) every day until he feels like committing horrible atrocities.
The correct answer is obviously “Ask your GM.” That aside, maybe you could convince a good or neutral cleric to raise undead, then Detect Evil? (Disclaimer: I have only a basic understanding of D&D mechanics, and the alignment system never made sense to me either.)
You’d probably need a neutral cleric to do that, but they’d have to be careful, since some DMs might make premediated casting of a [evil] spell simply to gain knowledge as something that would push a neutral individual over to evil.
… Spells are also categorically Good or Evil?
If said cleric casts that Evil spell, but does it unknowingly (e.g. mind control, or other more convoluted scenarios, perhaps involving magical sensory deprivation), are they still considered to have done an Evil act?
Yes, though it’s usually not much of an Evil act. More to the point, in most versions, clerics are prohibited from using opposed-alignment spells, which nicely insulates them from accidental alignment shifts due to spellcasting.
A good wizard, on the other hand, can actually cast protection from good (an evil spell) every day until he feels like committing horrible atrocities.
Yes, see for example in the 3.5 SRD how “Animate Dead” has the bracketed Evil after it here.