Hello!
If I understood this correctly, the answer is
"I made it a rule to forbear all direct
to the sentiments of others"
He refrained from directly contradicting other people's opinions.
"When another asserted something that I thought an error, I denied myself the pleasure of contradicting him abruptly, and of showing immediately some absurdity in his proposition;"
Although he wanted to contradict the man, he refrained from doing so. At least, not abruptly.
If I understood this correctly, the answer is
"I made it a rule to forbear all direct
He refrained from directly contradicting other people's opinions.
"When another asserted something that I thought an error, I denied myself the pleasure of contradicting him abruptly, and of showing immediately some absurdity in his proposition;"
Although he wanted to contradict the man, he refrained from doing so. At least, not abruptly.