I would say hypothesis. Then Conclusion. Then Theory. Then Principle. Then Fact. I'm not certain about the order, but I know, with a fair degree of certainty, lol, that hypothesis is the least certain.

I would say a theory is the least certain.

Hypothesis definitely because it hasn't been tested yet. A theory is more like a set of knowledge drawn from results.

Different people use those words differently. You'd have to ask each person individually. There is no consensus. Welcome to Earth. Fact would probably be the most certain of the lot. The problem is that some people consider a "fact" to be anything they feel uncomfortable being questioned about. On the other hand, other people consider a "fact" to be a direct observation. Most people consider a "theory" to be something that is guessed at but not proven. In science, however, a "theory" is often the highest degree of confidence you can obtain. Gravity is a theory. Things falling to the ground, that's a fact. A "conclusion" is only as certain as an "hypothesis". Sometimes the conclusion is less certain than the hypothesis, since the reasoning to derive the conclusion may have been faulty. A "principle" is neither certain or uncertain. It is only more or less useful as borne out by experience. In fact, you could say the same of the other four terms as well.

Hypothesis is without a doubt the least certain.

Hypothesis?....cuz you havta have a hypothesis, to create a theory...on the principal of a fact...and after study then you get the conclusion.

Hypothesis. You left out "conjecture" which is at the same level. The sure thing after that, is that "fact" is at the opposite end. The order of the rest of them is problematic: A "conclusion" is at the end of a chain of logic & is surely no stronger than any accepted assumption, conjecture, or whatever used along the way. A "principle" may have exceptions & the # to each one of them varies. The word "theory" has several different meanings ranging from "hypothsis" to the math meaning:a theorem is "something which has been proven",and so a theory is a set of theorems with the assumptions from which they follow. Many like to restrict it to the math meaning-which makes sense for clarification. Perhaps most well-known is the scientific theory: a logical connecting from empirical evidence.

I think most people answering this question have it backwards. (No offense -- sorry.) The lowest degree of certainty among these options would be a conclusion. I'm thinking of this in scientific terms. A fact is an observed data point (which may possibly have been inaccurately measured), upon which you construct a hypothesis, which you test by attempting to find a confirming fact, which if you do find, you construct a theory. Theories which stand the test of time can be categorized as principles. Facts could be inaccurately measured or observed, hypotheses are formulated on the basis of facts, hypotheses serve as the foundation for theories, and principles are constructed from previously validated theories. Each of these terms entails a degree of uncertainty. A conclusion is the only item on the list that presumes that you believe you know everything and cannot possibly be wrong. Since a conclusion requires reliance on every other thing on the list, and every other thing on the list entails some degree of uncertainty, and these degrees of uncertainty multiply each other down the chain, I would argue that a conclusion is the least reliable -- or should be expressed with the least degree of certainty.