The classic subjects are disciplines and each has specific concepts, skills, processes and requirements.  They are framed as pollinators – which fly between learners and teachers as established teachings of significance in developing an ‘educated’ mind.
Deep and broad learning requires these subjects to be integrated together so students understand them not just in isolation but also in context and via inter-connectedness. Schools are good at creating subject silos – separate specialist areas.
The disciplines outlined as ‘teachings’ have a history of knowledge garnered from cultural understanding and generations of refinement. The teacher needs to apply these in a modern context to ensure they remain relevant.