Estate planning is one of the areas of the law where the formalities matter immensely. Take proper will execution, for example, where one must have the right paperwork at the right time with appropriate witnesses in order for the will to be valid. It is not enough to simply tell someone your last wishes or even to have an attorney draw up a will. If it is not properly executed it will not be accepted by the court and enforced through the probate sytem.
Without a valid will, one's assets will pass through state laws governing "intestacy", meaning someone who has no last will and testament. The laws of intestacy are strict and that could result in one's assets being passed down to someone that you did not intend.
On the other hand, sometimes a person has created a will, but has not updated it in many years. It might seem obvious when life circumstances have changed that those wishes are no longer current, but without a validly executed new will, family members or friends named in the old one will not have to comply with more recently expressed wishes.
This is what happened in a recent case that is blending elements of estate planning with family law. In this case two men shared homes and a life together for nearly 20 years but were never married. When one of the men passed away from a terminal illness, his only will had been written and executed before the relationship started. And, although the two had been living and acting as if they were married, without legal recognition of the relationship and no newly executed valid will naming the man's partner, his assets are to be transferred to his sibilings.
In an effort to change this, the man's partner is asking to be declared his common law husband, which would entitle him to a share of the estate even though he was not named in the will.
Source: ABA Journal. "Gay man asks DC court to declare him common-law husband of deceased partner," Mark Hansen, Aug. 20, 2013.