We need to start, I think, by defining what a hood is used for, and the simple answer is that it is used to define the status of one’s membership within a corporation. Despite current practice, whereby each degree is seen as a discrete qualification, in the manner of A-levels, the original meaning of a degree was to mark one’s membership at bachelor or master/doctor level within a faculty – but not necessarily, I suspect, within any particular university; the hoods associated with the degrees meant ‘This chap is a member [of this university] at doctor level in the Faculty of Divinity.’ Indeed, the earliest hoods of Oxford and Cambridge (there is room for discussion over St Andrew’s, Glasgow and Aberdeen!) seem to have been identical – Doctors of Laws, for example, at both universities wore scarlet and pink. [Excerpt].
Groves, Nicholas (2002) "Who may wear the ‘Literate’s Hood’?," Transactions of the Burgon Society: Vol. 2.