theoretically; in theory
Used as an adverb to describe something that is true according to theory, but may not be realized in practice.
It's possible in theory, but difficult in practice.
noun which may take the genitive case particle 'no'
Used as a no-adjective to modify nouns, indicating that something is based on theory rather than practice.
This is merely a theoretical problem.
Compound of 理論 (theory) and 上 (from the viewpoint of).