| Pongidentheorie | Pongidae hypothesis |
| Mengentheorie | set theory |
| Knotentheorie | knot theory |
| Dramentheorie | dramatic theory |
| Graphentheorie | graph theory |
| Gruppentheorie | group theory |
| Quantentheorie | quantum theory |
| Wellentheorie | wave model wave theory |
| Zahlentheorie | theory of numbers |
| Spieltheorie | game theory |
| Pongidenhypothese | Pongidae hypothesis |
| Deszendenztheorie | descension theory evolutionary theory |
| Kategorientheorie | category theory |
| Automatentheorie | automata theory |
| Philanthropie | philanthropy |
| Eichtheorie | gauge theory |
| Poikilothermie | poikilothermy |
| Bindungstheorie | attachment theory |
| Hohlwelttheorie | hollow-Earth theory |
| Musiktheorie | music theory |