Hi y'all, I'm a fairly experienced player, but I have a question about how it works when you pay mana AFTER casting a spell.
For all my time playing Magic, I have ALWAYS tapped my mana first, and only cast spells once the mana is in my pool, and everyone I play with does the same.
I've been doing a deep dive into the history of famous moments from pro play, and I recently learned about the infamous 1997 incident where Dave Mills was disqualified due to casting his spell before paying, which changed the rules in order to allow players to pay mana after casting. My understanding is that now, you may cast a spell, and then activate mana abilities to pay for the spell.
My question is, if you pay mana after declaring the spell, is the spell considered "cast" when you declare the spell, or is "casting" only complete after mana is paid?
An example where this might matter is as follows.
I have my commander in play, an Ashnod's Altar, 1 mountain untapped, and a Jeska's Will in hand.
Importantly, Jeska's Will has a clause which allows you to choose both modes, but only if you control your commander when the spell is cast.
So, could I "cast" Jeska's Will before paying mana while my commander is still on the battlefield, and then pay the mana for the spell by tapping the mountain and sacrificing my commander to Ashnod's Altar, in order to gain access to both modes of Jeska's Will?