The concept of biological functionality can be a difficult one to formulate in the psychatric arena.
For instance, we can easily define functionality in cardiac matters -- funcitonality can be defined by exercise tolerance.
Similiarly, pulmonary function has specific quantitative measures.
How should we measure psychiatric functionality ?
Sigmund Freud measured this by evaluating, however, non quantiatively, the capacity to work and the capacity to engage in familial emotion. This suggestion does set some minimum goals of funcitonality.
Is there a better way ?
Of interest, Freud did not addres the problem from a moral, ethical, or philosophical perspective, which should trouble us, as he was not in any way unable to carry out such reasoning.
If we examine the problem in this latter fashion, we immediately encounter the problems that perhpas so intimidated Freud that he does not seem to have pursued the matter further.
If we consider the problem as a philosophical one, we are sure to encounter the problem we begin with - how do we measure functionality ?
The question taken from an existential perspective, can be met as either functionality within the scope of one's capacity (given a reasonable way of estimating that capacity), or instead, one's challenges.
The latter, if this becomes the focus, presents a much more severe challenge to the patient.
The former simply asks that we acheive whatever prosaic goal we set for the patient. The limited goal matches the limited capacity. However, this approach, in he end, brings us to the same problem. We will have patients who manifestly fail to achieve that which is in their capacity, and ask us, as physicians, to diminish what we might expect of them. Do we do them a disservice by doing so ?
If we do, then the task of psychiatry is a much larger one than what we might imagine it to be at the outset, one which Freud may have been, in his time and period (the advent of the Holocaust) to much of a pessimist to pursue. Should we pursue it today ? The specific challenge to psychiatry seems reasonable enough.
However, with even a brief review of the legal and social and political context, we see that this is a challenge. Expecting patients to fully engage towards their full potential as humans is, in its own way, a type of political dissent that is that of the most dangerous, the posing of a moral question that lays bare the moral impovershment of our larger society, including those most narcissistic about their moral stature.