It is important to understand that a person may have the legal capacity to make some decisions, but not others. For example, a person in a coma surely would not have the capacity to make any decisions. On the other hand, a person with Alzheimer’s, depending on its severity, may have the capacity to execute a will, but not sign a contact or make medical decisions.
If an incapacitated person purports to enter into a transaction, that transaction can be nullified by a court and anyone who improperly manipulated the incapacitated person into acting could be held liable. That is why it is important to consult with an elder law attorney, particularly when questions of capacity, including age-related cognitive decline and dementia, are involved.