Dark Confidant and split cards

On my upkeep controlling a Dark Confidant I trigger revealing a card and losing life to it's cmc cost. What happens if I have a split card with 2 identifiable spells? Do I get to choose which one I would prefer to lose my life on?

• Please link to cards (by using `[mtg:Card Name]`). – ikegami May 1 '13 at 14:26
• Don't use split cards with the new dark confidant vampire! – wesdfgfgd May 1 '13 at 14:34
• @wesdfgfgd Why not? Blood Scrivener only makes you lose 1 life, not life equal to the CMC. It would be abetter option that Dark Confidant. – SocioMatt May 1 '13 at 18:03
• @SocioMatt Blood Scrivener is the Dark Confidant Zombie. Wes is talking about Duskmantle Seer. – Alex P May 1 '13 at 18:28
• @AlexP Good call. It was the word "new" that threw me off. – SocioMatt May 1 '13 at 18:33

If it's somewhere other than on the stack or if it's fused, a split card's CMC is the sum of each half's CMC.

708.4. In every zone except the stack, the characteristics of a split card are those of its two halves combined. This is a change from previous rules.

708.4b The mana cost of a split card is the combined mana costs of its two halves. A split card’s colors and converted mana cost are determined from its combined mana cost.

Example: Assault/Battery’s mana cost is {3}{R}{G}. It’s a red and green card with a converted mana cost of 5. If you cast Assault, the resulting spell is a red spell with a converted mana cost of 1.

708.4b is rather poorly worded. As the example shows, the mana cost and converted mana cost of a split card is only the combined mana costs or converted mana costs of its two halves when it's not on the stack or when it's fused.

With the latest update to the comprehensive rules (June 5, 2017), the converted mana cost of split card is the sum of both halves. This happens to align with the previous "apply both answers" approach previously, but now split cards return a single answer instead of having to deal with "halves" of cards. From the rules:

708.4. In every zone except the stack, the characteristics of a split card are those of its two halves combined. This is a change from previous rules.

Specifically regarding CMC (emphasis mine):

708.4b The mana cost of a split card is the combined mana costs of its two halves. A split card’s colors and converted mana cost are determined from its combined mana cost.

Example: Assault/Battery’s mana cost is {3}{R}{G}. It’s a red and green card with a converted mana cost of 5. If you cast Assault, the resulting spell is a red spell with a converted mana cost of 1.