Adam, it all started in ancient Greece.
“In the western tradition (coming down from the ancient Greece), philosophy is the "mother" of all the knowledge, so doctor of philosophy refers to someone who is truly knowledgeable,” says Elena Hsu PhD’91, student services coordinator in the Graduate School.
As a reflection that a holder of a PhD has gained this higher level of education, it’s a university tradition to print master’s diplomas with a major and department, but not to include those fields on doctoral diplomas.
Diplomas all over the world have these same distinctions. As Hsu notes, when doctoral students are seeking jobs, they typically rely on their transcripts to reflect their coursework, not their diplomas.