And it is a fact that my social theory (which favours gradual and piecemeal reform, reform controlled by a critical comparison between expected and achieved results) contrasts with my theory of method, which happens to be a theory of scientific and intellectual revolutions. 
Charakteristisch für die deutsche Szene ist die Tatsache, daß ein breiter philosophischer Hintergrund für liberales Denken zu fehlen scheint oder daß jedenfalls Ideen dieser Art hierzulande kaum auf eine erhebliche Breiten- und Tiefenwirkung rechnen können. Die deutsche Ideologie bewegt sich zwischen Konservativismus und Revolution, zwischen unkritischer Hinnahme von Gegebenheiten und totaler Kritik am Gegebenen.
I am not in all cases and under all circumstances against a violent revolution. I believe with some medieval and Renaissance Christian thinkers who taught the admissibility of tyrannicide that there may indeed, under a tyranny, be no other possibility, and that a violent revolution may be justified. But I also believe that any such revolution should have as its only aim the establishment of a democracy; and by a democracy I do not mean something as vague as ‘the rule of the people’ or ‘the rule of the majority’, but a set of institutions (among them especially general elections, i.e. the right of the people to dismiss their government) which permit public control of the rulers and their dismissal by the ruled, and which make it possible for the ruled to obtain reforms without using violence, even against the will of the rulers. In other words, the use of violence is justified only under a tyranny which makes reforms without violence impossible, and it should have only one aim, that is, to bring about a state of affairs which makes reforms without violence possible.
I do not believe that we should ever attempt to achieve more than that by violent means. For I believe that such an attempt would involve the risk of destroying all prospects of reasonable reform. The prolonged use of violence may lead in the end to the loss of freedom, since it is liable to bring about not a dispassionate rule of reason, but the rule of the strong man. A violent revolution which tries to attempt more than the destruction of tyranny is at least as likely to bring about another tyranny as it is likely to achieve its real aims.
There is only one further use of violence in political quarrels which I should consider justified. I mean the resistance, once democracy has been attained, to any attack (whether from within or without the state) against the democratic constitution and the use of democratic methods. Any such attack, especially if it comes from the government in power, or if it is tolerated by it, should be resisted by all loyal citizens, even to the use of violence. In fact, the working of democracy rests largely upon the understanding that a government which attempts to misuse its powers and to establish itself as a tyranny (or which tolerates the establishment of a tyranny by anybody else) outlaws itself, and that the citizens have not only a right but also a duty to consider the action of such a government as a crime, and its members as a dangerous gang of criminals. But I hold that such violent resistance to attempts to overthrow democracy should be unambiguously defensive. No shadow of doubt must be left that the only aim of the resistance is to save democracy. [ch. 19, 414-5]
As a set of discoveries and devices, science has mastered nature; but it has been able to do so only because its values, which derive from its method, have formed those who practice it into a living, stable and incorruptible society. Here is a community where everyone has been free to enter, to speak his mind, to be heard and contradicted; and it has outlasted the empires of Louis XIV and the Kaiser. Napoleon was angry when the Institute he had founded awarded his first scientific prize to Humphry Davy, for this was in 1807, when France was at war with England. Science survived then and since because it is less brittle than the rage of tyrants.
This is a stability which no dogmatic society can have. There is today almost no scientific theory which was held when, say, the Industrial Revolution began about 1760. Most often today’s theories flatly contradict those of 1760; many contradict those of 1900. In cosmology, in quantum mechanics, in genetics, in the social sciences, who now holds the beliefs that seemed firm sixty years ago? Yet the society of scientists has survived these changes without a revolution, and honors the men whose beliefs it no longer shares. No one has recanted abjectly at a trial before his colleagues. The whole structure of science has been changed, and no one has been either disgraced or deposed. Through all the changes of science, the society of scientists is flexible and single-minded together, and evolves and rights itself.