# It's difficult to be rigorous about whether a machine really knows or thinks, because we're… by John McCarthy > "It's difficult to be rigorous about whether a machine really knows or thinks, because we're hard put to define these things." > **— John McCarthy**, *The Little Thoughts of Thinking Machines (1983), excerpt candidate* Verification Status: Unverified — exact wording/source has not yet been independently confirmed against a primary source; source clue: The Little Thoughts of Thinking Machines (1983), excerpt candidate.