Unnatural wills are not illegal per se unless they infringe upon public policy. Further, many jurisdictions allow the variation of wills which do not properly provide for dependents, such as spouses and children.
In Abel v Dickinson, Justice Fogleman of the Supreme Court of Arkansas wrote:
"The expression unjust and unnatural will is usually applied when a testator leaves his estate, or a large portion of it, to strangers, to the exclusion of natural objects of his bounty without any apparent reason.
"A will cannot be said to be unnatural because a testator preferred one for whom she had developed a close and affectionate relationship, or when the natural objects of the testator's bounty are in no need of funds, aid or assistance.
"A will is unnatural in the legal sense only when it is contrary to what the testator would have been expected to make in the light of his feelings and intentions at the time, even though they may be prejudiced, however much it may differ from the ordinary actions of people in similar circumstances."
In the Estate of Lacey case, the Supreme Court of Oklahoma held:
"The will of the testator was an unnatural will. He left the bulk of his estate to one child, Agnes Mielke, to the exclusion of his seven other children. While not conclusive, an unnatural disposition of property by the testator may be considered in determining his testamentary capacity.
"The fact that the will is unjust or unnatural does not of itself establish testamentary incapacity, but it is a circumstance which may be considered in connection with other evidence, and which may have weight in determining the capacity of the testator; and an unnatural or unjust disposition coupled with other evidence indicating incapacity may justify a verdict against the will.
"It is natural for a person to make provisions in his will for those who were particularly close and helpful to him during his lifetime, and more especially, to those within his own family. In some instances, where one member of the family has completely devoted his efforts and energies to the care and attention of a testator, it is only natural that this one be preferred in the will. But in the instant case the record does not show any particular reason, purpose or motivation for the testator to devise the bulk of his estate to his daughter, Agnes Mielke, and to disinherit his other children."