irrealizable

Irrealizable is an adjective meaning not capable of being realized or actualized. In English, it is relatively rare and most often appears in specialized discussions within philosophy, logic, computer science, and planning. It is used to describe plans, goals, propositions, or states that cannot be realized within a given framework, system, or set of constraints.

The term often carries a nuance that emphasizes intrinsic impossibility under the specified conditions rather than mere impracticality. For example, a plan may be irrealizable if the available resources or governing rules make its execution impossible; a specification may be irrealizable if no constructive implementation can satisfy it within a model. In logic and computer science, realizability concepts relate to the existence of witnesses or programs; an irrealizable proposition would be one for which no such witness exists in the considered context.

Etymology: the word is formed by the prefix ir- meaning not, attached to realizable from realize. It is closely related to unrealizable, though irrealizable tends to be used in more technical or context-specific discourse. Related terms include infeasible, impossible, and achievable in contrast to possible or realizable.

In summary, irrealizable marks a stronger claim than mere impracticality, signaling that, given the relevant constraints, realization is impossible.