On paper might be one of the most commonly used phrases in the English language, often used to describe something that looks great in theory, but may not necessarily translate well in reality. However, there are plenty of other ways to express this concept using different words and phrases. One alternative is "in theory," which implies that something has been carefully thought out and should work in practice, but there are unknown variables that could potentially affect the outcome. Another option is "on the surface," which suggests that something appears to be good at first glance, but deeper analysis could reveal flaws or issues that weren't immediately apparent. Other synonyms for on paper include in principle, theoretically, and hypothetically.