Unanswerable describes a question that cannot be answered, either because no answer exists or because finding the answer is impossible with current knowledge.

Some questions are unanswerable because they don't make logical sense, like “What does the color blue taste like?” or “What happens when an unstoppable force meets an immovable object?” These questions seem to ask something, but they mix up categories in ways that make answering them impossible.

Other questions are unanswerable because we simply don't have enough information yet. “Are we alone in the universe?” might be unanswerable right now, but future discoveries could change that. Scientists often work on questions that seem unanswerable until someone finds a breakthrough.

Still other questions are unanswerable because they ask about things we can never know. “What was I thinking about exactly one year ago at this moment?” Unless you wrote it down, that information may be lost forever.

Teachers sometimes include unanswerable questions on tests by accident, maybe leaving out crucial information: “How many apples did Sarah have?” without saying whether she bought more or gave some away. Recognizing when a question is unanswerable shows you understand what information is actually needed to solve a problem.