If I'm a Seeker of the Song 2 (Complete Arcane, p. 56) and War Chanter 5 (Complete Warrior, p. 87), can I play 3 Bardic Musics at once? I seemingly can.
The Potential Rule
I have actually done some more research and I think I found the answer in an unlikely place, Unearthed Arcana. It is Unearthed Arcana, so take it for what it is, but it has this passage in a sidebar:
Multiclassing And Variant Classes
Multiclassing between variants of the same class is a tricky subject. In cases where a single class offers a variety of paths (such as the totem barbarian or the monk fighting styles), the easiest solution is simply to bar multiclassing between different versions of the same class (just as a character can't multiclass between different versions of specialist wizards). For variants that are wholly separate from the character class—such as the bardic sage or the urban ranger—multiclassing, even into multiple variants of the same class, is probably okay. Identical class features should stack if gained from multiple versions of the same class (except for spellcasting, which is always separate).
It does include the caveat "from multiple versions of the same class" . But I think this is a suggestion that class features should stack, except spellcasting. It is possible that the text included in many prestige classes regarding the stacking of sneak attack, turn undead and Uncanny Dodge, is the version of this rule that they eventually ended up with given UA's playtest/pseudo-house rule status.
While UA certainly is fraught with dubious rulings, we have no ruling of how class features stack/don't stack in the general sense. We have certain specific instances, but no general rule. UA provides the closest thing to a general rule, and hints at RAI, but it is itself a specific rule as pointed out in the comments.
Applying it to the question
Here are the two instances of Combine Song, first from Seeker of Songs and then from War Chanter
Combine Songs (Ex): A seeker of the song of 2nd level or higher can combine two types of bardic music or seeker music to provide the benefits of both. The seeker chooses two music abilities and activates both using the same standard action. If either or both require concentration, the seeker can maintain concentration on both by using one standard action each round to concentrate. The normal stacking rules for bonus types apply to music abilities combined with this ability.
Combine Songs (Su): A war chanter of 5th level or higher with 12 or more ranks in any Perform skill can combine two types of bardic music or war chanter music to provide the benefits of both (normal stacking rules for bonus types apply).
In putting these side by side I notice two things, that I think actually make them different abilities that, unfortunately, have the same name.
- Type of Ability: Seeker of Song's is an Extraordinary ability, where as War Chanter's is a Supernatural ability
- Ability requirements: Both require levels but only War Chanter requires ranks in perform.
If they are separate abilities, they definitely stack. If not...
I would say that given the absence of a RAW for whether class features outside of those that have specificstack, we have to make judgement call based on RAI which is ultimately up to the DM.
I think that it is clear that they do stack, given that every specific rule we have says that the specified abilities stack.
Each adds the ability to combine a song from that class with bardic music or another song from that class. Notice that both abilities don't cancel out the bardic music, they simply add an aditional affect via another song. Thus allowing you to add both Warchanter music and Seeker Songs to the same bardic music.
The RAW do lead to some interesting restrictions on what musics can be combined.
The following combinations are legal
- 3 Bardic Musics,
- 1 Seeker Song, 2 Bardic Musics
- 2 Seeker Songs
- 2 Warchanter Songs
- 1 Warchanter Song, 2 Bardic Musics
- 1 Warchanter Song, 1 Bardic Music, 1 Seeker Song
But these are not legal, due to the fact that both specify combining Bardic Music and their respective songs.
- 1 Seeker Song, 1 Warchanter Song
- 2 Seeker Songs, 1 Warchanter Song
- 2 Warchanter songs, 1 Seeker Song
- 3 Seeker Songs
- 3 Warchanter Songs
As a general rule, effects of the same name doesn't stack unless explicitly called out as doing so. Both Seeker of the Song and War Chanter can play and additional song when using the Combine Songs class feature (same name), so to my understanding they probably don't stack.
Whats stacks is a tricky question.
Bonus Types of the same name explicitly doesn't stack, as descriped on page 171 of the Players Handbook and elaborated in the Dungeon Masters Guide on page 22. Some exceptions like Dodge Bonus though.
In the same vein, Magical effects is also called out on page 171 as not stacking, giving examples of overlapping and negating cases.
Feats aren't explicitly stated as not stacking ( In the books that i can find. The DND Wiki says If a character has the same feat more than once, its benefits do not stack unless indicated otherwise in the description. ), but i would argue that since some feats makes it explicit that they can be taken more than once, non-stacking is probably "Rules-As-Intended".
Nothing is explicitly calling out class features, but based on the above, i would say that "Rules-As-Intended" they do not stack.
However this is probably up to your DM since it isn't in any book i can find.