The general test for soundness of mind is whether the person making the Will understood:

• The meaning and effect of the Will;
• What he/she owned, and
• Who the people are to whom he/she is leaving his/her belongings.

If you are not of sound mind, and someone later challenges the validity of your Will, the judge could rule that the document is invalid. This kind of ruling is rare, but it does happen.

Laws differ from state to state, but generally, if someone contests the Will by claiming the deceased was not of sound mind, that person must prove, by a “preponderance of the evidence”--which means one side must be considered more provable than the other-- that the deceased lacked mental capacity. The executor or proponent of the Will must then show, “beyond a reasonable doubt”--convincing to a moral certainty--that the deceased did have the required mental capacity in order for the Will to be held valid. Both sides rely upon the testimony of medical doctors and may present the deceased’s medical records, but they may also present other evidence, such as eye witness testimony from those who had contact with the deceased before, during, and/or after the execution of the Will.

New Mexico case law only requires a “lucid moment”—if, at the moment the person who signed the Will, met the three requirements, the requirements of testamentary capacity were satisfied, even if the person did not recall making the Will the next day! States’ laws may differ so check with an estate attorney in your state.

Your mental condition at the time you signed your Will is what is legally relevant. If you suffer from any mental disorder, from depression to dementia, or there are doubts about your mental capacity, evidence, such as a letter from your doctor, should be left with your Will to prove you were mentally competent at the time you signed the Will. Otherwise, your Will may be open to challenge.

Though challenges are rare-- less than 4% of wills are ever challenged—but when it does happen, the challenge is usually made by relatives who feel the Will is unfair or doesn't reflect how the deceased person intended to distribute property. All or part of a Will may be challenged by anyone named in it or by any family member who would be entitled to a share under state law if the Will were declared invalid.

You should contest a Will in probate court if you have reason to doubt its validity, but to make a challenge, you must have a legitimate stake in the estate. A challenge should also be based on solid discrepancies, not on your personal opinion of how property should have been distributed.

Since courts tend to uphold Wills offered to probate, challenges rarely succeed. At any point, parties can end a challenge by agreeing to “pay off” the person challenging the Will. This sometimes happens when the Will has disinherited the challenger. If no such agreement intervenes, the court decides the validity of the Will.