The essence of the Liberal outlook lies not in what opinions are held, but in how they are held: instead of being held dogmatically, they are held tentatively, and with a consciousness that new evidence may at any moment lead to their abandonment.  Bertrand Russell (1872-1970), British philosopher, mathematician. "Philosophy and Politics," Unpopular Essays (1950).

Eccentricity has always abounded when and where strength of character has abounded; and the amount of eccentricity in a society has generally been proportional to the amount of genius, mental vigour, and moral courage which it contained.  John Stuart Mill (1806-1873), British philosopher, economist. On Liberty, ch. 3 (1859).

"Argument ...  does not remove doubt, so that the mind may rest in the sure knowledge of the truth, unless it finds it by the method of experiment.... For if any man who never saw fire proved by satisfactory arguments that fire burns ... his hearer's mind would never be satisfied, nor would he avoid the fire until he put his hand in it ... that he might learn by experiment what argument taught."  Roger Bacon (c. 1214-1294), British philosopher, scientist. Opus Maius, pt. 4, ch. 1 (1267).

you cannot make a theory scientific simply by trying to find facts that might be explained by the theory. You have to try to find facts that could only be explained by the theory, and this means that you should try to show that no rival theory could explain those same events. A theory is meaningfully proposed as a scientific theory only if the proposer is willing to look seriously at rival theories that have some claim to explain the same events, in order to determine whether those theories do not do a better job. Jan Garrett, philosophy professor at Western Kentucky University, "The Enigmatic Origins of the Jung Cult" (1999).