Just a few quotes that I came across in the last couple of days.
[In contemplation,] if a man will begin with certainties, he shall end in doubts; but if he will be content to begin with doubts, he shall end in certainties.
-- Francis Bacon, in The Advancement of Learning.
Amartya Sen paraphrases yet another (complex) passage by Francis Bacon:
"The registering and proposing of doubts has a double use," Bacon said. One use is straightforward: it guards us "against errors". The second use, Bacon argued, involved the role of doubts in initiating and furthering a process of inquiry, which has the effect of enriching our investigations. Issues that "would have been passed by lightly without intervention." Bacon noted, end up being "attentively and carefully observed" precisely because of the intervention of doubts.
This quote is from Nietzche (taken from this article by Scott McLemee):
Objection, evasion, joyous distrust, and love of irony are signs of health. Everything absolute belongs to pathology.
Reading them reminded me of what Richard Feynman said in a lecture "The Uncertainty of Science" long time ago (it's the first essay in The Meaning of It All):
If we were not able or did not desire to look in any new direction, if we did not have a doubt or recognize ignorance, we would not get any new ideas. There would be nothing worth checking, because we would know what is true. So, what we call scientific knowledge today is a body of statements of varying degrees of certainty. Some of them are most unsure; some of them are nearly sure; but none is absolutely certain. Scientists are used to this. We know that it is consistent to be able to live and not know. [...]