In Florida, as in most states, it has long been emphasized that the right to dispose of one's property by Will is highly valuable and it is the policy of the law to hold a Last Will and Testament good wherever possible. Not uncommonly, disgruntled beneficiaries sometimes challenge a Will on the grounds that the person who executed the Will (known as either the Testator if a man or a Testatrix if a woman) did not have testamentary capacity. In other words, they allege that the person's mental state was such that they could not validly sign a Will.
In Florida, to have testamentary capacity means that a Testator is of "sound mind" which has been described as having the ability to mentally understand in a general way (1) the nature and extent of the property to be disposed of, (2) the Testator's relation to those who would naturally claim a substantial benefit from his Will, and (3) a general understanding of the practical effect of the Will as executed. As can be seen from these considerations, the standard only requires a general understanding.
A Testator may still have testamentary capacity to execute a valid Will even though he may frequently be intoxicated, use narcotics, have an enfeebled mind, failing memory, or]vacillating judgment. Moreover, an insane individual or one who exhibits unusual conduct may execute a valid Will as long as it is done during a lucid interval. This lucid interval may be short-lived but if it existed at the time the Will is signed, then the Testator was of sound mind and may sign the Will.
With this understanding in mind, it can be seen that a person with illness, dementia, and even Alzheimers could validly execute a Will so long as at the time of the signing, the person had a lucid moment sufficient to understand the three items described above.