What characterises science on this view is a social decision to allow the world to correct our ideas, and collateral decisions to eschew attempts to insulate those ideas from inconsistency and counter-example. Those decisions are implemented socially in institutions that entrench rules of procedure or method. Thus and only thus is a demarcation established between folk wisdom, social and political opinions and the like, all equally institutional, and science. The difference is not in the results – the claims about the world that issue from time to time from actors in the institutions. Indeed, these may at times look (misleadingly) similar. It lies in the methods by which work proceeds, where method here is construed not simply as a bunch of methodological rules, which is how it is usually presented, but as the deliberate choice and tailoring of methodological rules to specified aims. The choice is institution-building rather than personal. Science is to be identified with an institutionalised aim or set of aims, together with the institutional rules and practices that have been devised to foster pursuit of these aims. These rules serve specifiable purposes and are subject to revision depending upon whether they accomplish such purposes. (Yet Popper did not discuss the reform of scientific institutions, even though he sometimes deplored what science had become (Popper 1972).) It is these rules that enable science to pursue the goals of being objective, realistic, in touch with experience, explanatory, progressive, and causal. Obedience to these rules is what makes the institutions of science different from other social institutions, including those of pseudo-science, magic, logic, and mathematics. It is not doctrines, ideas, or sentences that are scientific or non-scientific; it is certain institutionalised ways of handling doctrines, ideas, and sentences that are scientific or non-scientific. The outcome of this effort is not guaranteed truths, but hypotheses that stand at the end of a chain of conjecture and refutatìon. The main result of the investigation is that we have a deeper and more humbling sense of the underlying problems than that with which we started. 
It is not unscientific to make a guess, although many people who are not in science think it is. Some years ago I had a conversation with a layman about flying saucers—because I am scientific I know all about flying saucers! I said “I don’t think there are flying saucers”. So my antagonist said, “Is it impossible that there are flying saucers? Can you prove that it’s impossible?” “No”, I said, “I can’t prove it’s impossible. It’s just very unlikely”. At that he said, “You are very unscientific. If you can’t prove it impossible then how can you say that it’s unlikely?” But that is the way that is scientific. It is scientific only to say what is more likely and what less likely, and not to be proving all the time the possible and impossible. [165-6]
[I]t would often be expedient, for the purpose of getting over some momentary embarrassment, or attaining some object immediately useful to ourselves or others, to tell a lie. But inasmuch as the cultivation in ourselves of a sensitive feeling on the subject of veracity, is one of the most useful, and the enfeeblement of that feeling one of the most hurtful, things to which our conduct can be instrumental; and inasmuch as any, even unintentional, deviation from truth does that much towards weakening the trustworthiness of human assertion, which is not only the principal support of all present social well-being, but the insufficiency of which does more than any one thing that can be named to keep back civilisation, virtue, everything on which human happiness on the largest scale depends; we feel that the violation, for a present advantage, of a rule of such transcendant expediency, is not expedient, and that he who, for the sake of a convenience to himself or to some other individual, does what depends on him to deprive mankind of the good, and inflict upon them the evil, involved in the greater or less reliance which they can place in each other’s word, acts the part of one of their worst enemies. Yet that even this rule, sacred as it is, admits of possible exceptions, is acknowledged by all moralists; the chief of which is when the withholding of some fact (as of information from a malefactor, or of bad news from a person dangerously ill) would save an individual (especially an individual other than oneself) from great and unmerited evil, and when the withholding can only be effected by denial. But in order that the exception may not extend itself beyond the need, and may have the least possible effect in weakening reliance on veracity, it ought to be recognised, and, if possible, its limits defined; and if the principle of utility is good for anything, it must be good for weighing these conflicting utilities against one another, and marking out the region within which one or the other preponderates. [ch. II, 181]
Diese spekualtiven Welten sind, wie in der Kunst, Produkte unserer Phantasie, unserer Intuition. Aber in der Wissenschaft werden sie von der Kritik kontrolliert: Die wissenschaftliche Kritik, die rationale Kritik, ist von der regulativen Idee der Wahrheit geleitet. Wir können unsere wissenschaftlichen Theorien niemals rechtfertigen, denn wir können nie wissen, ob sie sich nicht als falsch herausstellen werden. Aber wir können sie kritisch überprüfen: An die Stelle der Rechtfertigung tritt die rationale Kritik. Die Kritik zügelt die Phantasie, ohne sie zu fesseln. 
I think that science works by a careful balance of two apparently contradictory impulses. One, a synthetic, holistic, hypothesis-spinning capability, which some people believe is localized in the right hemisphere of the cerebral cortex, and an analytic, skeptical, scrutinizing capability, which some people believe is localized in the left hemisphere of the cerebral cortex. And it is only the mix of these two, the generating of creative hypotheses and the scrupulous rejection of those that do not correspond to the facts that permit science or any other human activity, I believe, to make progress.