What is necessary for a subsequent document to revoke a previous will?

For a subsequent document to effectively revoke a previous will, it must be a contemporaneous writing executed by the testator. This is important because the law requires clear intent to revoke a will for such an action to be legally recognized. A contemporaneous writing means that the document is created at the same time as or after the previous will and explicitly indicates the testator's intention to revoke the earlier will.

This requirement is in place to ensure that there is no ambiguity regarding the testator's desires concerning the distribution of their estate after their death. A will typically must meet certain formalities, such as being written, signed, and, in many jurisdictions, witnessed, to ensure its validity. Therefore, simply having an oral agreement or an informal declaration, as suggested in the other options, would not suffice to demonstrate the necessary legal intent or formality.