Thus, truthfulness necessarily entails righteousness, just as lying necessarily entails wickedness. When the antecedent—striving to be truthful—is present, its necessary consequence—righteousness—is present. When the necessary consequence—righteousness—is absent, the antecedent—truthfulness—is absent. When lying, the antecedent, is present, wickedness, its necessary consequence, is present. When the necessary consequence—wickedness—is absent, the antecedent—lying—is absent. Hence, a man’s lack of righteousness is taken as evidence of his lying, and his freedom from wickedness as evidence of his truthfulness.

The upright person described by the jurists is someone free of wickedness, meaning the commission of a major sin or persistence in a minor sin. When these are absent in him, so too is the lying that leads him to such wickedness. The evildoer is someone who lacks righteousness; when his righteousness is absent, his truthfulness is absent as well. The inference drawn from this hadith rests on the premise that what prompts righteousness necessarily entails righteousness, and what prompts wickedness necessarily entails wickedness.

Error is thus like forgetfulness, and deliberate action is like lying. And Allah knows best.