Dispel via opposite spells

Question

This question was developed as an extension of one that is related.

What interests me in particular is the part about dispeling.
I'm totally agree with the linked answer to that related question (provided by someone from Pathfinder staff, I believe). That answer is true for Haste vs Slow (and vise versa), as they explicitly dispel each other.

But what if it is Darkness vs Light? Or any other pair of spells, one of wich can dispel the other, but the other can't dispel the first one?

Why it is assumed that dispeling with opposite spell is a separate use of spells from both such pairs?

Cons:

1. I found no evidence of necessity of using a dispelling spell in some unusual manner to accomplish said dispel (opposite to counterspelling, wich has it's own mechanic). So I assume that dispelling is the part of a normal casting (opposite to counterspelling, again).

   Example of application:
   Both spells (cast normally) must simply affect the same target. And now both spells are affecting the same target and interact with each other. And, if in case of Haste vs Slow, Slow dispels Haste and Haste dispels Slow (leaving nothing in the end), in case of Darkness vs Light, Darkness dispels Light, but Light has no effect on Darkness. And thus Darkness isn't dispeled and stays on the object.

2. Were the dispel function a specific use of a dispelling spell, the spell, used that way, shouldn't than affect anything but targets with the spells to be dispeled. But it is said nowhere in the rules.

   Example of application:
   We have a party of four characters: A, B, C, and D. A and B are hasted. C and D are not. When an evil sourcerer casts slow on them (and they all fail their saves), A's and B's hasted condition is dispelled, while C and D are slowed.

Are those cons wrong and why? What pros it has?

Answer 1

I doubt strongly that Darkness is wasted to simply dispel Light with no additional effect.

Sorry to disappoint.

You have to specifically use darkness to dispel or counter a light descriptor spell.

Light spells are not dispelled "automatically" by the radiating darkness created by the normal usage of the darkness spell. This was a major change in 5e, where that is exactly the case. To use darkness to counter or dispel a light spell in 3.5 or Pathfinder, you have to expend the spell casting to only counter or dispel the one light spell you're targeting, just like a targeted use of dispel magic. Unlike dispel magic, no check is required, however; the dispel happens instantly.

If objects with light spells cast on them of lower level are taken into an area of magical darkness, they stop emitting light while in that darkness, but the spell is not dispelled. If the light spell is of equal or higher level, then the darkness is partially illuminated by your light source. This creates a sort of "surrounded by thick fog" effect, where a person carrying a magical torch (say, with 3rd level continual flame cast on it in a fog of 2nd level darkness) would be able to see around them in the torch's radius, but beyond that point is pitch black darkness.

A note about semantics in rulebooks, and inferring "RAW".

This was the specific issue that the OP ended up having, so I will clarify it here in full for others. In the spell description for darkness, in the d20SRD, here's the exact wording:

Darkness counters or dispels any light spell of equal or lower spell level.

Notice how it doesn't say "Darkness can be used to counter or dispel any light spell". Taken completely out of context, the most logical interpretation is that upon casting the spell darkness, countering or dispelling is included with the standard shadowy-illumination effect of darkness for free. That is not the case.

As a counter-example, consider the logical conclusion of this interpretation. It says that darkness "counters or dispels," so that means that when you cast the spell, you can counter someone's light spell for free, or you can have the radiating darkness dispel light magic. Does the first option sound weird? That's because it is; no spell in D&D that I know of allows you to counterspell and generate normal effects simultaneously. If such spells exist, that would be clarified in the description explicitly. That's just how counterspelling fundamentally works. In fact, the rules on counterspelling state that "both spells negate each other with no results," (from the Pathfinder Core rules) so such a spell would require a very clearly denoted mention that the spell's normal effects persist through the counterspelling. Therefore, we can infer that the best interpretation is that counterspelling is a separate usage, and since the statement is written such that counterspelling and dispelling are bound by the exact same rules, dispelling must also be a separate usage.

Rulebooks are often terrible at semantics, and I haven't looked at the original 3.5 rules in ages but if my hunch is correct, the statement was written differently outside of the d20SRD. Look for consistency in the rules and choose what obeys that consistency; don't pick apart an individual statement. This statement is written in the exact same format for every spell with the same effect. For instance, hallow's spell description reads that it "counters but does not dispel unhallow." It's the same formatting. Even if it's not clear, the meaning is consistent, and we know that through usage of very consistant verbage, the same sort of ruling is applied across all spells that contain this sentence.

Answer 2

So, there are effectively three separate ways to use darkness with respect to light:

1. Counterspell the casting of light with darkness. This involves readying an action, and causes both spells to be wasted with no effect.

   Darkness can be used to counter

   This is a separate use for darkness, an alternative to just casting the spell. When used this way, countering is all the spell does.

   If counterspelling were a free part of darkness along with its usual effects, it would not be described as an alternate use; it would just be an effect along with all of the others.

2. Dispel an existing light effect by casting darkness. In this case, darkness works like a dispel magic that only affects light, and automatically succeeds. There is no darkness effect created when using darkness in this manner.

   Darkness can be used to [...] dispel

   Again, an alternate use for the spell: instead of using the spell for its usual effects, you can instead use it to dispel. When used this way, dispelling (removing the light effect) is all it does.

   If dispelling were a free part of darkness along with its usual effects, it would not be described as an alternate use; it would just be an effect along with all of the others.

3. Just cast darkness, and allow its effect to overwhelm the light effect. Specifically, from the darkness spell description:

   Magical light sources only increase the light level in an area if they are of a higher spell level than darkness.

   So if you cast darkness in the same area in which a light effect can be found, darkness “wins” and applies its effect, smothering the effect of light. There is a darkness effect caused by this route, but the light effect also remains. This matters if, say, the darkness effect were to be dispelled: the underlying light would then shine through.

Each of these is an option, and you may use whichever of them is most suitable for your purposes. There might be reasons why you want to remove a light effect, not just hide it, or reasons why you want to remove light without going so far as to cause darkness (say, you have Darkvision and your foes don’t, so you use darkness to remove their light, and then you can see and they can’t – if you actually cast darkness for its effect, you wouldn’t be able to see either).