Affinity is a keyword ability.
- 702.40a. Affinity is a static ability that functions while the spell is on the stack. "Affinity for [text]" means "This spell costs you less to cast for each [text] you control."
- 702.40b. The affinity ability reduces only the amount of generic mana a spell's controller has to pay; it doesn't reduce how much colored mana that player has to pay.
- 702.40c. If a spell has multiple instances of affinity, each of them applies.