impossible

Impossible is a term describing something that cannot be done, cannot occur, or cannot be true. The concept is distinguished by different notions of impossibility: logical impossibility, physical impossibility, and practical impossibility. Logically impossible propositions entail a contradiction and cannot be true in any circumstance (for example, a square circle). Physical impossibility refers to events prohibited by the known laws of nature, such as perpetual motion or faster-than-light travel under current physics. Practical impossibility refers to events that are not logically ruled out but are exceedingly unlikely or require resources or conditions beyond what is available.

Philosophers and scientists use the idea of possibility and impossibility to analyze claims about what could be the case. In modal logic and possible-world semantics, a proposition is impossible if it is false in every possible world. The notion of an "impossible world" is a theoretical device used in some arguments, though it remains debated in philosophy.

Etymology: The word "impossible" comes from Middle English impossibel, from Old French impossible, ultimately from Latin impossibilis, formed from in- "not" + possibilis "able to be done" (from posse "to be able").

Usage: In everyday language, something is described as impossible when it cannot be done under current knowledge or circumstances. The term also appears in culture and media—"Impossible" is a common title or theme for songs, films, and books, reflecting aspiration, challenge, or contradiction.