كبدن الإنسان للطب، والكلمة والكلام لعلم النحو
As the human body is the subject of medicine, and word and speech are the subjects of grammar.
Medicine: examines conditions such as health and disease in relation to the body. A particular treatment is not the whole subject matter of medicine.
Grammar: examines words and connected utterances, including syntactic relations and inflection. Its field is linguistic structures, not the human body.
These examples distinguish what a science studies from its title or one of its practical benefits.