One Spanish composition textbook I taught from once had a section on degrees of certainty. Basically, the idea was that you could do any one of three things in any particular sentence: simply assert one's conclusions, assert them with a phrase like "sin duda" [without a doubt] that affirmed one's certainty, or assert them with a qualifier that implied some degree of doubt. The idea is to calibrate one's own relation to the subject matter by distinguishing between what needs to be reinforced as a certainty, what can simply be stated baldly as a fact, and what needs more qualification. There is a whole spectrum of rhetorical possibilities.
Now obviously I knew how to calibrate degrees of certainty before seeing this textbook, but I had never really sat down to analyze the phenomenon before. The purpose of this calibration, I believe, is to reassure the reader that you have thought about how you know what you know, to what degree or extent, how much you are putting yourself out on a limb.
One exercise might be to write a paragraph, interpreting a very difficult text, with no markers of degree of certainty at all. What's the problem? If it's a difficult text, then you can't really be sure of every aspect of your interpretation, so now add some qualifications. Ok, but there are some parts of the interpretation that are pretty solid, so add some anti-qualfiers here, like of course, or without a doubt. Leave some statements unmarked for degree of certainty: that's like the zero degree of something that can be asserted without rhetorical reinforcement.
Ironically, the strongest statements are those without any marker of certainty. It would sound odd to say, "Without a doubt, I am writing these words in 2010." The negation of doubt implies doubt in such a case. Why would anyone think differently?