Perhaps better said as the "fields of knowledge". I'm wondering whether there is a single word that describes fields of learning or knowledge. The word should work in the following sentences (where I've used cognitum and cogniti as fictitious placeholders for the singular and plural forms, respectively).
"upon examination of the various cogniti, we can see common…"
"Among the cogniti of classical education, I find Mathematics to be of great interest. As a cognitum it serves as the basis for all other cogniti; the universe itself is a consequence."