Can a split card be cast for both halves at the same time?

Split cards have two separate halves printed on a single card, but under normal rules you choose exactly one half to cast. Each half is its own spell with its own mana cost, type, and effect. This is governed by CR 708.2, which states that when casting a split card, you choose one of its halves to cast.

The only exception is the Fuse keyword (CR 702.101). Cards like Breaking // Entering from Dragon's Maze carry the Fuse ability, which grants an additional option: you may cast both halves simultaneously by paying the combined total mana cost. The resulting spell counts as a single spell that resolves both effects when it resolves.

If a split card does not have Fuse, you simply pick Left or Right and cast only that half. The other half is ignored for casting purposes, though both halves' characteristics are considered when the card is anywhere other than the stack (e.g., in a graveyard, hand, or exile), per CR 708.3.

Concrete example: You control a Fire // Ice (no Fuse). You cannot pay 1R + 1U to cast both halves at once. You must choose: cast Fire (1R — deal 2 damage split) OR cast Ice (1U — tap a permanent and draw a card). Only the chosen half becomes a spell on the stack.

By contrast, if you cast Beck // Call (which has Fuse), you may pay 1G + 3WU to cast both halves simultaneously, placing a single fused spell on the stack that will create tokens and trigger the card-draw effect when it resolves.