“All cats fly; Tom is a cat; so Tom flies — it's sound.”
Usage Entry 1183 / 1350 60-second read
Valid vs. Sound
A well-formed logical argument versus valid argument with true premises.
The comparisoni
“All cats fly; Tom is a cat; so Tom flies — it's valid (logically well-formed) but not sound (premise is false).”
The ruleii
¶
VALID = form. SOUND = form + truth.
A VALID argument is one where if the premises are true, the conclusion must follow — purely a structural check. A SOUND argument is valid and has true premises. All sound arguments are valid; not all valid arguments are sound.
Memory aidiii
Remember it like this
Valid = structure. Sound = structure + facts.