Matthew's Journal

No, though there is an overlap. If all the details about mental illnesses had been discovered, which I don't believe to be even nearly the case, it just might be possible to determine accurately what types of mental illness would or would not be likely to impair someone's ability to make a rational decision.

At the present level of knowledge, it is probably possible to make estimates in many cases as to whether someone is completely off with the fairies and has little perception of what most people perceive as reality, or whether the person is able to properly consider a serious decision. If the prospect of imminent and painful death causes you to be depressed, I would not expect that that would, of itself, prevent someone from making a rational and informed decision. As rational as life ever gets, anyway.