Stage 6 of LOGOSGBITS: seven trials in the difference between a good form and true content. An argument can reason perfectly from falsehoods, or reach a true conclusion by pure luck. Only where valid form meets true premises — soundness — are you obliged to believe the conclusion.
Each trial is locked until you clear the one before it. Every level scores out of 1000 — 600 for accuracy, 400 for speed — so speed alone can't clear the bar; you have to solve most problems, and quickly. Reach 650 to unlock the next.
You can judge a form without consulting the world and the world without consulting the form, refuse to be impressed by a true conclusion, tell soundness from mere validity — and name the one combination logic forbids: a valid argument with true premises can never deliver a false conclusion.