Mathematics is organised around numerous "big theories": group theory, topology, linear algebra, etc. Distinguishing characteristics of a big theory include: a clearly defined object of study, and some "big theorems", such as characterisations of structures of a certain kind (e.g. the classification of finite simple groups) or identification of normal forms.
Do we have analogous "big theories" in computer science? What are they? Do they provide an organisational structure for our subject (including teaching)? If the answer to any of these questions is "no", does it matter?
I will briefly introduce the above ideas and then open the floor for discussion.