اعلم أن لكل علم وصناعة غاية وإلا لكان طلبه عبثا والجد فيه لغوا
Know that every science and craft has an aim; otherwise seeking it would be purposeless and striving in it fruitless.
A science’s subject matter answers what it investigates, while its aim answers what is sought by that investigation.
For medicine, the human body is the subject, while healing and the preservation of health are among its purposes. Likewise, the content logic studies must be distinguished from the benefit sought through that study.