An Apprentice of Prime understands the formation of spells and the creation of an Imago well enough to attack it on a direct, metaphysical level, allowing her a great deal more defensive capability.
The mage may use Counterspell on any Awakened spell.
The player rolls Gnosis + Prime when the character does not know the Arcanum used, or when this would be a higher dice pool than the appropriate Arcanum.
The mage may also spend a point of Mana to Counter a spell’s lowest Arcanum rather than its primary Arcanum.
For example, a mage with this Attainment Countering a Fate 4, Space 2 spell may pay a point of Mana to roll the Clash of Wills against Gnosis + Space instead of Gnosis + Fate.