To discover to the world something which deeply concerns it, and of which it was previously ignorant; to prove to it that it had been mistaken on some vital point of temporal or spiritual interest, is as important a service as a human being can render to his fellow-creatures […]. [ch. II, 36]
Discussion and the growth of ideas
The Western rationalist tradition, which derives from the Greeks, is the tradition of critical discussion–of examining and testing propositions or theories by attempting to refute them. This critical rational method must not be mistaken for a method of proof, that is to say, for a method of finally establishing truth; nor is it a method which always secures agreement. Its value lies, rather, in the fact that participants in a discussion will, to some extent, change their minds, and part as wiser men.
It is often asserted that discussion is only possible between people who have a common language and accept common basic assumptions. I think that this is a mistake. All that is needed is a readiness to learn from one’s partner in the discussion, which includes a genuine wish to understand what he intends to say. If this readiness is there, the discussion will be the more fruitful the more the partners’ backgrounds differ. Thus the value of a discussion depends largely upon the variety of the competing views. Had there been no Tower of Babel, we should invent it. The liberal does not dream of a perfect consensus of opinion; he hopes only for the mutual fertilisation of opinions and the consequent growth of ideas. 
Explanation as the antidote to extremism
The challenge in an election season that largely takes place in the form of 30-second advertisements and fire-up-the-base rallies is that rarely is anybody — candidate or voter — asked to explain his or her positions. American political discourse, in short, is not discourse at all.
So what can be done to turn it into one? The answer implied by our research is not that we should all become policy wonks. Instead, we voters need to be more mindful that issues are complicated and challenge ourselves to break down the policy proposals on both sides into their component parts. We have to then imagine how these ideas would work in the real world — and then make a choice: to either moderate our positions on policies we don’t really understand, as research suggests we will, or try to improve our understanding. Either way, discourse would then be based on information, not illusion. […]
Strong opinion and vigorous debate are key parts of democracy and the foundation to American culture. Yet most people would agree that it is not productive to have a strong opinion about an issue that one doesn’t really understand. We have a problem in American politics: an illusion of knowledge that leads to extremism. We can start to fix it by acknowledging that we know a lot less than we think.
Strengthening your opponent’s case
Throughout the history of advocacy and controversy the approach even of polemicists of genius, like Voltaire, has been to seek out and attack the weak points in an opponent’s case. This has a severe disadvantage. Every case has weaker as well as stronger parts, and its appeal lies, obviously, in the latter; so to attack the former may embarrass its adherents but not undermine the considerations on which their adherence largely rests. This is one of the reasons why people so rarely change their views after losing an argument. More often such a reverse leads eventually to a strengthening of their position, in that it leads them to abandon or improve the weakest parts of their case. It often happens that the longer two intelligent people go on arguing the better each side’s case becomes, for each is being all the time improved as a result of criticism. The Popperian analysis of this is self-evident. What Popper aims to do, and at his best does do, is to seek out and attack an opponent’s case at its strongest. Indeed, before attacking it he tries to strengthen it still further. He sees if any of its weaknesses can be removed and any of its formulations improved on, gives it the benefit of every doubt, passes over any obvious loopholes; and then, having got it into the best-argued form he can, attacks it at its most powerful and appealing. This method, the most intellectually serious possible, is thrilling; and its results, when successful, are devastating. For no perceptible version of the defeated case is reconstructable in the light of the criticism, every known resource and reserve of substance being already present in the demolished version. [91-2]
Defending the indefensible
Popper setzte dem Neomarxismus Marcuses sein Konzept der „offenen Gesellschaft“ entgegen, deren zentrale Merkmale die freie Diskussion und Institutionen seien, die „den Schutz der Freiheit und der Schwachen“ garantieren. Von einer Unterdrückung oder von antagonistischen Klassengegensätzen in den westlichen Ländern zu sprechen, lehnte er ab. Von seiner positiven Einschätzung der USA rückte er auch angesichts des Vietnamkriegs nicht ab. Er wies vielmehr darauf hin, dass es die Opposition innerhalb der USA gewesen sei, die die Regierung zu dem Eingeständnis gezwungen habe, dass der Vietnamkrieg ein großer Fehler gewesen sei. Genau dieser Einfluss der Opposition aber weise die USA als eine offene, zur Selbstkorrektur fähige Gesellschaft aus. Popper vergaß auch nicht zu erwähnen, dass es gerade die westliche Demokratie sei, die es den Neomarxisten erlaube, ihre Ideen zu verbreiten. Der von den Marxisten behaupteten Ohnmacht und Determination des Individuums durch gesellschaftliche Verhältnisse setzte er die Überzeugung entgegen, dass der Mensch mithilfe der Vernunft die Gesellschaft verändern kann und dass die politische Macht in der Lage ist, die ökonomische Macht zu kontrollieren. 
The success of science
Der ungeheure wissenschaftliche Fortschritt in den letzten Jahrhunderten ist vor allem wohl darauf zurückzuführen, daß in diesem Bereich der Hang zur Dogmatisierung immer wieder überwunden werden, daß sich die Tradition des kritischen Denkens in der Konkurrenz der Ideen und Argumente immer wieder durchsetzen konnte. Die in diesem Bereich oft vorherrschende positive Akzentuierung neuer und kühner Ideen, eine entsprechende Einstellung der relativen Unvoreingenommenheit und Irrtumstoleranz, bei der der Andersdenkende meist nicht als Ketzer diffamiert, sondern oft sogar als willkommener Diskussionspartner betrachtet wird und man bereit ist, unter Umständen von ihm zu lernen, findet in anderen Bereichen, vor allem da, wo institutionell verankerte ideologische Bindungen bestehen, im allgemeinen keine Entsprechung.
The final decade of the second millennium saw the theory of democracy take a strong deliberative turn. Increasingly, democratic legitimacy came to be seen in terms of the ability or opportunity to participate in effective deliberation on the part of those subject to collective decisions. (Note that only the ability or opportunity to participate is at issue; people can choose not to deliberate.) Thus claims on behalf of or against such decisions have to be justified to these people in terms that, on reflection, they are capable of accepting. The reflective aspect is critical, because preferences can be transformed in the process of deliberation. Deliberation as a social process is distinguished from other kinds of communication in that deliberators are amenable to changing their judgements, preferences, and views during the course of their interactions, which involve persuasion rather than coercion, manipulation, or deception. The essence of democracy itself is now widely taken to be deliberation, as opposed to voting, interest aggregation, constitutional rights, or even self-government. The deliberative turn represents a renewed concern with the authenticity of democracy: the degree to which democratic control is substantive rather than symbolic, and engaged by competent citizens. 
What Popper argued is that a problem classically treated as logical (the demarcation of science) is insoluble in that form. Yet science does seem distinctive, i.e. demarcatable. The solution to its distinctness is found in its institutionalised rules of inquiry. These rules can be circumvented without violating any rules of logic. In the choice or decision not to circumvent them we find the hallmark of science. Such choice is not individual but social: it is constitutive of and dependent upon institutions. Moreover, being institutions, the rules of science are not like rules of inference: discoveries about the properties of logical systems. Institutional rules can be assessed against given aims, such as fruitfulness, and be discussed and modified. Science and its distinctiveness are open to modification. 
Science’s social framework
Science is a special kind of endeavour. Philosophers have been seeking to specify in what ways it is special for almost four hundred years (at least since Francis Bacon). Karl Popper is known for his attempt to characterise it negatively, as refutable conjectures about the world. But this is not the sum of what he said. What is and is not refutable requires discussion, which is a social process; if conjectures about the world are to be refuted a social framework is needed for their testing. Popper’s negative method requires institutions and traditions.