Why are some traditional subjects plural in form?
Most ic words are plural in form and singular in meaning.
Physics, mathematics, linguistics, politics, statistics.
When those words are used as adjectives, they’re singular or add al. Physical, mathematical, political, statistical, linguistic (NOT al).
Two of the oldest ic words are singular:
Rhetoric, logic.
Subjects that don’t end in ic are mostly singular.
All ometry, ology, ography words are singular, along with language, literature, history.
Some of these may be plural when it makes sense. Analytic geometry teaches one useful type of geometry. Non-euclidean geometries teaches about several useless mythical types of geometry. Department of language discusses language in general, while Department of languages teaches students to speak German, Russian, French, etc.
Newer two-word subject names have another irrational singular vs plural. When the second word is science the name is singular. When the second word is study the name is plural. Social science vs social studies. Political science vs political studies.
As a first approximation, Greek names are singular, Latin names are plural, more recent names are variable.
Polistra's Mill 