(BY AVICENNA)
Medicine considers the human body as to the means by which it is cured
and by which it is driven away from health. The knowledge of anything,
since all things have causes, is not acquired or complete unless it
is known by its causes. Therefore in medicine we ought to know the
causes of sickness and health. And because health and sickness and
their causes are sometimes manifest, and sometimes hidden and not to be
comprehended except by the study of symptoms, we must also study the
symptoms of health and disease. Now it is established in the sciences
that no knowledge is acquired save through the study of its causes and
beginnings, if it has had causes and beginnings; nor completed except
by knowledge of its accidents and accompanying essentials. Of these
causes there are four kinds: material, efficient, formal, and final.
Material causes, on which health and sickness depend, are—the affected
member, which is the immediate subject, and the humors; and in these
are the elements. And these two are subjects that, according to their
mixing together, alter. In the composition and alteration of the
substance which is thus composed, a certain unity is attained.
Efficient causes are the causes changing and preserving the conditions
of the human body; as airs, and what are united with them; and
evacuation and retention; and districts and cities, and habitable
places, and what are united with them; and changes in age and
diversities in it, and in races and arts and manners, and bodily and
animate movings and restings, and sleepings and wakings on account of
them; and in things which befall the human body when they touch it, and
are either in accordance or at variance with nature.
Formal causes are physical constitutions, and combinations and virtues
which result from them.
Pinal causes are operations. And in the science of operations lies the
science of virtues, as we have set forth. These are the subjects of
the doctrine of medicine; whence one inquires concerning the disease
and curing of the human body. One ought to attain perfection in this
research; namely, how health may be preserved and sickness cured. And
the causes of this kind are rules in eating and drinking, and the
choice of air, and the measure of exercise and rest; and doctoring with
medicines and doctoring with the hands. All this with physicians is
according to three species: the well, the sick, and the medium of whom
we have spoken.