Stacking modifiers

I'm considering playing a bladesinger wizard in an upcoming campaign. I noticed something, and I'm not sure of how this works so I'm asking here.

One of the benefits of a Bladesong says:

Focus. When you make a Constitution saving throw to maintain Concentration, you can add your Intelligence modifier to the total.

One of the new feats in Arcana Unleashed, the Conjuration Adept says:

Persistent Conjuration. While maintaining Concentration on a spell from the Conjuration school, you gain a bonus to Constitution saving throws to maintain this Concentration. This bonus is equal to the ability modifier of the score increased by this feat.

Of course, I would add +1 to Intelligence if I take that feat.

So, does this mean if I cast a Conjuration spell, and I have to make a save to maintain concentration, while Bladesong is active, I get to add my Intelligence modifier TWICE?? They are two different features. So, do they stack?

Yep, they'd stack as they use different wording. One says you can add your Intelligence modifier and the other says you gain a bonus equal to your Intelligence modifier. 

The reason this matters if "you can add your Intelligence modifier" by itself doesn't stack if you have it multiple times, whereas a specific bonus that's equal to a modifier does stack.

Modifiers can stack, effects can't. The only modifier that is explicitly disallowed to stack is the Proficiency Bonus.
All other modifiers can stack so long as they don't come from the same effect.

Quote from Davyd >>

The reason this matters if "you can add your Intelligence modifier" by itself doesn't stack if you have it multiple times, whereas a specific bonus that's equal to a modifier does stack.

Is there an actual rule that says this anywhere?

There's a rule that says this about your proficiency bonus, but I don't think there's one that says it about ability modifiers.

Quote from Natrel >>

Modifiers can stack, effects can't. The only modifier that is explicitly disallowed to stack is the Proficiency Bonus.
All other modifiers can stack so long as they don't come from the same effect.

I don't think it's even that restrictive. There's no general rule that says modifiers from multiple instances of the same effect can't stack. There is a specific rule about that for spells, but not for other effects. The lack of such a general rule is why things like "Slow" weapon mastery property have specific language saying they don't stack.

Quote from wagnarokkr >>

Quote from Davyd >>

The reason this matters if "you can add your Intelligence modifier" by itself doesn't stack if you have it multiple times, whereas a specific bonus that's equal to a modifier does stack.

Is there an actual rule that says this anywhere?

There's a rule that says this about your proficiency bonus, but I don't think there's one that says it about ability modifiers.

 It's the wording. If you have two things that say "you can add your Y to X", they're both satisfied by adding X to Y once and only once because they're saying you can perform the action A where A is "Add X to Y"

However, if something says "you gain a bonus to X where the bonus is equal to Y", you can stack that because each instance of gaining a bonus is satisfied independently.

Think of it this way, if you have a coupon that says "You can get one free side per purchase of a main course" it doesn't matter if you have three of those coupons, you can only redeem it once. However, if you have a coupon that says "Redeem for one free side when purchasing a main course", you could redeem multiple of those.

Quote from Davyd >>

Quote from wagnarokkr >>

Quote from Davyd >>

The reason this matters if "you can add your Intelligence modifier" by itself doesn't stack if you have it multiple times, whereas a specific bonus that's equal to a modifier does stack.

Is there an actual rule that says this anywhere?

There's a rule that says this about your proficiency bonus, but I don't think there's one that says it about ability modifiers.

 It's the wording. If you have two things that say "you can add your Y to X", they're both satisfied by adding X to Y once and only once because they're saying you can perform the action A where A is "Add X to Y"

I understand what you're saying, but I am not seeing why, if I have two features that both say I can perform the action A, I can't perform the action A twice, regardless of what A is. There are lots of situations where you can have multiple features that tell you to do the same thing, and I think it's generally understood that in those cases you can do it multiple times. If that weren't the case, then there wouldn't be a need for the explicit rule saying that your Proficiency Bonus can't ever be added to something more than once.