Quite the innocent question as it doesn't seem to serve any purpose except roleplay, but I'd like to address these questions for the sake of ... science. And also because a player brought the project up :
1 - Do Intelligent items possess a soul, or rather some sort of artificial intelligence?
2 - Does a Magus' blackblade, while clearly defined as a sentient magical weapon, count as a familiar for the purpose of the Soulswitch spell?
3 - If it does, how is it represented in game terms? Does the character's mental stats change to represent the Blackblade's, for example? Would the blackblade be bonded enough to be able to use the Magus' abilities?
4 - And should such a shenanigan happen, should a DM take over the "Possessed Magus" until the true self comes back as a standard action? After all, the blackblade should be considered a NPC.
Intelligent Items Flavor Text
Magic items sometimes have intelligence of their own. -->Magically imbued with sentience, these items think and feel the same way characters do and should be treated as NPCs.<--
Soulswitch
Targets : -->you and your familiar<--
You may only cast this spell if you currently have a familiar. You place your soul into the body of your familiar, and your familiar's soul is placed in your body. This functions as if you possessed your familiar using magic jar; your familiar simultaneously possesses your body in the same manner. You can't freely transfer your soul between your body and your familiar's—if you choose to return to your body as a standard action, the spell ends. If either body is killed, both spirits return to their original bodies, the spell ends, and the original owner of the slain body dies.
Blackblade
At 3rd level, the bladebound magus’ gains a powerful sentient weapon called a black blade, whose weapon type is chosen by the magus (see sidebar). A magus with this class feature cannot take the familiar magus arcana, and cannot have a familiar of any kind, even from another class.
A black blade is bonded to a particular magus, -->much like a familiar<--, but in more of a partnership than a master-servant relationship.
Souls are in general a very questionable term as far as rules.
That doesn't really matter though, because being much like a familiar isn't a familiar. The blackblade is not a valid target for soulswitch.
If it were a valid target however, the answers to your further questions would be that it is exactly the same as if the black blade was a familiar. Being 'bonded' doesn't change the base concept from Magic Jar that spells and spell-like abilities etc. are not accessible by the possessing entity. And while a black blade indeed is a class feature that is also an NPC, so in fact is a familiar. Most DMs pretty much let the players control this sort of class feature, but they are all in fact non-player characters.
Being 'bonded' doesn't change the base concept from Magic Jar that spells and spell-like abilities etc. are not accessible by the possessing entity.
I had missed that vital piece of info. Thanks for the thorough response!
1) It's possible to create intelligent items without a soul. So all of it really depends on the flavor of your blackblade.
2) A blackblade is technically not a familiar, so soulswitch wouldn't work.
3) If you treat it as a familiar, then it has all the stats that a familiar of your class level would have. It wouldn't have any of your class features.
4) Your familiar is typically a character you control, not the GM. So if the familiar takes over your body, you control them. However, blackblades are a little different because they have an Ego. I'd probably say that the player can play the blackblade while they possess their body unless the GM calls for an Ego check and the magus fails it.
