I made it a rule to forbear all direct contradictions to the sentiments of
others, and all positive assertion of my own. I even forbade myself the use
of every word or expression in the language that imported a fixed opinion,
such as "certainly", "undoubtedly", etc. I adopted instead of them "I
conceive", "I apprehend", or "I imagine" a thing to be so or so; or "so it
appears to me at present".

When another asserted something that I thought an error, I denied myself the
pleasure of contradicting him abruptly, and of showing him immediately some
absurdity in his proposition. In answering I began by observing that in
certain cases or circumstances his opinion would be right, but in the present
case there appeared or seemed to me some difference, etc.

I soon found the advantage of this change in my manner; the conversations I
engaged in went on more pleasantly. The modest way in which I proposed my
opinions procured them a readier reception and less contradiction. I had
less mortification when I was found to be in the wrong, and I more easily
prevailed with others to give up their mistakes and join with me when I
happened to be in the right.
-- Autobiography of Benjamin Franklin