Infiniti2000 said:
It does not reduce it in all cases, such as for deciding what spells you can cast.
You can't really put "explicitly" at the start of a list which includes "and other details".
Your remaining questions are a non sequitur. I can't even understand their relevance to this topic, let alone your quote of mine.
If your level is used in a calculation, it is treated as one lower.
If this level refers to class level, then we have, for the ranger, a calculation using that level to determine caster level; his caster level is class level divided by 2. We have, for the cleric, a calculation, where his caster level is his class level plus 1. We have, for the multiclass Wiz/Ftr, a calculation, where his caster level is his wizard class level + 4, capped at his hit dice. The sorcerer's caster level is, in this case, his class level - it's a very simple calculation, but since his caster level is derived from his class level, it's a calculation nonetheless.
And when level is used in a calculation, it's treated as one lower.
So the caster level of a 6th level paladin is 6 / 2 = 3. The caster level of a 6th level paladin with one negative level is [6-1] / 2 = 2.
The caster level of a 4th level cleric with the Good domain when casting a [Good] spell is 4 + 1 = 5. The caster level of the same cleric with one negative level is [4-1] + 1 = 4.
The caster level of a 5th level sorcerer is 5 = 5. The caster level of a 5th level sorcerer with one negative level is [5-1] = 4.
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If the level referred to is not class level, but rather caster level, then there's no need to prove anything.
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If the level referred to is not class level, but rather character level, then the clause doesn't have a whole lot of effect; it's not very often that character level is used in a calculation. How many uses of Bardic Music do you have per day? Independent of character level, only dependent on class level. How much damage does a paladin deal on a Smite Evil? Independent of character level, only dependent on class level.
-Hyp.