When do you have to declare the use of Fortitude and Potence?

Question

The 20th anniversary edition of Vampire, The Masquerade says that you have to declare the use of any Disciplines at the start of your turn (P. 271), but then in some casses like Potence, it is written that you may reflexively spend a blood point to active it, and I'm not sure what that means.

About Fortitude, in Vampire, The Dark Ages 20th anniversary edition says that "Once per turn, she may spend a blood point to automatically soak her Fortitude in damage, instead of adding it to her Stamina." The Masquerade book doesn't even mention the possibility of activating Fortitude wich makes me question if they just forgot to mention it or if they intentionally removed this perk.

The ideal use of Potence would be to activate it only if you hit your target and Fortitude only when you're hit, but I'm not sure if that's how it works.

So, when do I have to/can declare to activate these Disciplines?

Answer 1

1. As defined on page 513 of the V20 rules, a reflexive action is one that doesn't count as a separate action for the purposes of split die pools. It means that activating it doesn't penalize your attack roll, but you still must do so at the start of your turn.

2. The rules for Vampire: Dark Ages 20th Edition were written years after and separately from the V20 rules. Accordingly, the ability to spend blood on Fortitude was neither forgotten nor omitted; it simply didn't exist. Many of the disciplines in the two books have different rules and differing levels; this is intentional to reflect an era when Kindred were more powerful. You or your Storyteller should decide which rules are in play, but one should not assume cross-compatibility. In this case, the Fortitude spend modifies a soak roll, which only happens when damage takes place. You'd spend that when the damage is inflicted.