In Scots law, adults are presumed to have legal capacity to enter into contracts and to dispose of their property as they see fit. That presumption may be rebutted where an individual's mental condition impairs that capacity. This has been the legal position for some time. The text reproduced here is taken from the written pleadings drawn up by an eminent seventeenth-century advocate for a client who sought to resist a claim on his deceased sister's estate. It was argued by the other side that she had been incapacitated by mental illness before her death and at the time that she had made provision. The pleading expounds Scottish seventeenth-century notions of insanity in a particular context, and argue for a way of determining whether a person had the necessary capacity by using and drawing on earlier Continental texts. It is notable that there is use of medical evidence almost a century prior to the first recognized use of medical testimony as to mental disorder in English courts.