709.3 A player chooses which half of a split card they are casting before putting it onto the stack.
709.3a
Only the chosen half is evaluated to see if it can be cast. Only that half is considered to be put onto the stack.
709.3b
While on the stack, only the characteristics of the half being cast exist. The other half’s characteristics are treated as though they didn’t exist.
709.3c
An effect may create a copy of a split card and allow a player to cast the copy. That copy retains the characteristics of the two halves separated into the same two halves as the original card. (See rule 707.12.)
(refs: 707.12)