فلا يبحث الطبيب عن بدن الإنسان من حيث إنه موجود
The physician does not investigate the human body merely insofar as it exists.
Existence is a very general predicate shared by countless things. That alone does not specify medical questions such as health, weakness, or disease.
Changing the respect of inquiry changes the scientific question. That is why a subject must be considered with the properties proper to its discipline.