How should a summoner synthesist calculate his saving throws?

Question

How should a Summoner Synthesist calculate his saving throws? i.e. at level 5 the Eidolon has strong saves Fort +4 Refl +4 and weak save Will +1, while Summoner has Fort +1 Refl +1 and Will +4, Additionally, at level 2 Shielded Meld special ability grants +2 to all saves. Therefore we have been adding all since they are a "fused creature." i.e. Fort (+4, +1, +2) = +7, Refl (+4, +1, +2) = +7, Will (+1, +4, +2) = +7

The synthesist uses the eidolon’s base attack bonus, and gains the eidolon’s armor and natural armor bonuses and modifiers to ability scores.

RAW never specifically addresses saves - although we assumed that eidolon's weak saves were weak because summoner's were strong and visa versa. However, it occurs to me that these may not stack just like resistance spell and a cloak of resistance don't stack. Should we just be using the eidolon's saving throws for the abilities CON, DEX, since we are using those modifiers?? i.e. +6, +6, AND the summoner's WIS +6
OR use the which ever is highest bonus rule such as with multiple enhancement bonuses - take the higher one at level 5 also +6, +6, +6?

Answer 1

The synthesist gets nothing from the eidolon's saves, and only part of its ability scores.

From the PFSRD:

Fused Eidolon
...
While fused with his eidolon, the synthesist uses the eidolon’s physical ability scores (Strength, Dexterity, and Constitution), but retains his own mental ability scores (Intelligence, Wisdom, and Charisma). ... The synthesist uses the eidolon’s base attack bonus, and gains the eidolon’s armor and natural armor bonuses and modifiers to ability scores.

There's nothing in there about saves. If something gives the eidolon a bonus to saves (such as the progression eidolons get as the summoner gains levels), the summoner gains no benefit from it. It doesn't matter which saves are the eidolon's good saves: the synthesist does not get those bonuses.

A synthesist will tend to have higher saves than other summoners though, thanks to ability scores. Because she uses her eidolon's Dexterity and Constitution ability scores, she will use its modifiers in those abilities rather than her own (which are likely to be lower). This will tend to give her higher reflex and fortitude saves than she would otherwise have.

Shielded Meld (which kicks in at level 4, incidentally, not level 2) does improve the synthesist's saves, because it explicitly says it does.

Thus, a level 4 summoner would calculate her saves as follows (while fused with her eidolon):

• Fortitude: +1(summoner) +C(eidolon's Con modifier) +2(shielded meld)
• Reflex: +1(summoner) +D(eidolon's Dex modifier) +2(shielded meld)
• Will: +4(summoner) +W(synthesist's Wis modifer) +2(shielded meld)

(Plus any other bonuses, such as from magic items, feats, traits, etc.)

TLDR: Synthesists are already ridiculously broken; don't make it worse by giving them bonuses to saves they're not supposed to be getting.