Historical Rules · 18 June 2010
Rule 601.2
Official source text from the 18 June 2010 Rules release
To cast a spell is to take it from where it is (usually the hand), put it on the stack, and pay its costs, so that it will eventually resolve and have its effect. Casting a spell follows the steps listed below, in order. If, at any point during the casting of a spell, a player is unable to comply with any of the steps listed below, the casting of the spell is illegal; the game returns to the moment before that spell started to be cast (see rule 715, "Handling Illegal Actions"). Announcements and payments can't be altered after they've been made.