With Magic, you must be very cautious about your terminology. Not solely what Hackworth says in his (very right) reply, but in addition what “play a” means. As an illustration, what you truly stated in your second paragraph:
Does taking part in that card rely as the primary spell?
is true (okay, if being fully right, you “solid” spells, you “play” lands, so “Does casting that card rely as the primary spell?”). In the event you solid Clarion Spirit as your first spell of a flip (and it resolves), after which solid one other spell, Clarion Spirit’s potential will set off.
Word (because the Gatherer ruling states) should you solid a spell, after which solid Clarion Spirit (and it resolves), the set off will not occur, as a result of the creature was not on the battlefield at solid time, when the set off would occur.
However as Hackworth says, triggered talents should not spells. Activating activated talents will not be casting a spell.
