In theory is a set phrase that is used to describe something that is based on a concept or principle, which may or may not be proven true in practice. There are several synonyms for the term "in theory," including theoretically, hypothetically, abstractly, ideologically, and conceptually. These words indicate that something is based on an idea, a belief, or a hypothesis rather than on tangible evidence or actual experience. They suggest that there is some degree of uncertainty or speculation involved in the statement, and that it may not necessarily reflect reality. These synonyms can be useful in academic writing, where the distinction between theory and practice is often a central concern.