Founding the Third Path — ruling 1

If you cast a card “without paying its mana cost,” you can’t choose to cast it for any alternative costs. You can, however, pay additional costs. If the card has any mandatory additional costs, you must pay those to cast the card.

Founding the Third Path — ruling 2

If the card has {X} in its mana cost, you must choose 0 as the value of X when casting it without paying its mana cost.

Founding the Third Path — ruling 3

You must pay all costs for the copy of a spell you cast as Founding the Third Path’s last chapter ability resolves. If you choose to cast it, you must cast as the ability resolves. You can’t wait and cast it at a later time.

Founding the Third Path — ruling 4

As a Saga with read ahead enters the battlefield, its controller chooses a number from one to that Saga’s greatest chapter number. The Saga enters the battlefield with the chosen number of lore counters. Neither choosing the number nor putting the counters on the Saga use the stack, and neither can be responded to.

Founding the Third Path : règles, fonctionnement et interactions (MTG)

Founding the Third Path is one of those cards players keep asking about. Here is, in plain words, what its official text says, the rulings published by Wizards of the Coast, and the combos players actually run.

Official card text

Read ahead (Choose a chapter and start with that many lore counters. Add one after your draw step. Skipped chapters don't trigger. Sacrifice after III.) I — You may cast an instant or sorcery spell with mana value 1 or 2 from your hand without paying its mana cost. II — Target player mills four cards. III — Exile target instant or sorcery card from your graveyard. Copy it. You may cast the copy.

How it works : Founding the Third Path

Original English text — Wizards of the Coast / Scryfall

#1September 9, 2022· Wizards of the Coast
If you cast a card “without paying its mana cost,” you can’t choose to cast it for any alternative costs. You can, however, pay additional costs. If the card has any mandatory additional costs, you must pay those to cast the card.
No other card is named in this ruling.
#2September 9, 2022· Wizards of the Coast
If the card has in its mana cost, you must choose 0 as the value of X when casting it without paying its mana cost.
No other card is named in this ruling.
#3September 9, 2022· Wizards of the Coast
You must pay all costs for the copy of a spell you cast as Founding the Third Path’s last chapter ability resolves. If you choose to cast it, you must cast as the ability resolves. You can’t wait and cast it at a later time.
No other card is named in this ruling.
#4September 9, 2022· Wizards of the Coast
As a Saga with read ahead enters the battlefield, its controller chooses a number from one to that Saga’s greatest chapter number. The Saga enters the battlefield with the chosen number of lore counters. Neither choosing the number nor putting the counters on the Saga use the stack, and neither can be responded to.
No other card is named in this ruling.