Untenable means impossible to defend, maintain, or continue because the facts or logic don't support it. When a position is untenable, you simply can't make it work no matter how hard you try.

Imagine arguing that 2 + 2 equals 5. No matter how confidently you present your case, the math proves you wrong. Your position is untenable. Or picture a castle built on crumbling cliffs: as the ground erodes, defending it becomes untenable, no matter how many soldiers you station there.

The word often appears in debates and arguments. If someone's excuse for missing homework keeps changing and contradicting itself, their story becomes untenable. When a scientist's theory conflicts with solid evidence, other scientists will call it untenable. In chess, when your king is surrounded with no good moves left, your position has become untenable.

The opposite of untenable is tenable: defensible, logical, possible to maintain. A tenable argument has facts and reasoning behind it. An untenable one collapses under scrutiny, like a sandcastle hit by waves. Sometimes people cling to untenable positions out of pride or stubbornness, but eventually reality catches up with them.