The phrase "more aforethought" contains two distinct elements - "more" and "aforethought." Antonyms for the word "more" could include "less," "decrease," or "diminish." The term "aforethought" can be defined as something that is premeditated or considered in advance, so antonyms could include "spontaneous," "impulsive," or "unplanned." A potential phrase that could serve as an antonym for "more aforethought" could be "less impulsive" or "reduce premeditation." In any case, the opposite of "more aforethought" would involve acting or speaking without much forethought or advance planning.