We must love them both, those whose opinions we share and those whose opinions we reject, for both have labored in the search for truth, and both have helped us in finding it.Attr. St. Thomas Aquinas
This seems to be the quote du jour for the feast of St. Thomas this year (e.g., in eye-wrenching typography from Word on Fire). But is it authentic?
Yes and no and sort of. After poking around for a bit, I found a good treatment of the question.
TL;DR: It’s attributed to “a commentary on Aristotle” all over the Internet, but St. Thomas wrote a lot of those. I managed to track it down (via the above link) to Sententia super Metaphysicam 12.9.14 (2566). It turns out the the saint is quoting Aristotle, who said this:
And if anyone in treating this subject should be found to form a different opinion from the one stated here, we must respect both views but accept the more certain
Alternative translation: and if those who apply themselves to these matters come to some conclusion which clashes with what we have just stated, we must appreciate both views, but follow the more accurate.
It seems to me that the more accurate view is that Aristotle and St. Thomas are referring to opinions rather than directly to people.
So (a) it’s a statement which St. Thomas is endorsing rather than something that he came up with on his own; (b) it refers to opinions and not to people (IMHO).