The difference between Utopian and piecemeal engineering turns out, in practice, to be a difference not so much in scale and scope as in caution and in preparedness for unavoidable surprises. … [W]hile the piecemeal engineer can attack his problem with an open mind as to the scope of the reform, the holist cannot do this; for he has decided beforehand that a complete reconstruction is possible and necessary. 
According to this piecemeal view, there is no clearly marked division between the pre-scientific and the scientific experimental approaches, even though the more and more conscious application of scientific, that is to say, of critical methods, is of great importance. Both approaches may be described, fundamentally, as utilizing the method of trial and error. We try; that is, we do not merely register an observation, but make active attempts to solve some more or less practical and definite problems. And we make progress if, and only if, we are prepared to learn from our mistakes: to recognize our errors and to utilize them critically instead of persevering in them dogmatically. Though this analysis may sound trivial, it describes, I believe, the method of all empirical sciences. This method assumes a more and more scientific character the more freely and consciously we are prepared to risk a trial, and the more critically we watch for the mistakes we always make. …
For the piecemeal technologist or engineer these views mean that, if he wishes to introduce scientific methods into the study of society and into politics, what is needed most is the adoption of a critical attitude, and the realization that not only trial but also error is necessary. And he must learn not only to expect mistakes, but consciously to search for them. We all have an unscientific weakness for being always in the right, and this weakness seems to be particularly common among professional and amateur politicians. But the only way to apply something like scientific method in politics is to proceed on the assumption that there can be no political move which has no drawbacks, no undesirable consequences. To look out for these mistakes, to find them, to bring them into the open, to analyse them, and to learn from them, this is what a scientific politician as well as a political scientist must do. Scientific method in politics means that the great art of convincing ourselves that we have not made any mistakes, of ignoring them, of hiding them, and of blaming others for them, is replaced by the greater art of accepting the responsibility for them, of trying to learn from them, and of applying this knowledge so that we may avoid them in future. [80-1]
An die Stelle einer Begründung oder Rechtfertigung im klassischen Sinne tritt hier die komparative Analyse alternativer Vorschläge für die Lösung der betreffenden Probleme auf der Grundlage regulativer Ideen, das heißt: bestimmter Wertgesichtspunkte, die der Entscheidung – das heißt: der Selektion der im Sinne dieser Ideen besten Lösung – zugrundegelegt werden können. Das ordnungspolitische Problem – die Frage nach der Beschaffenheit einer adäquaten Sozialordnung – läßt sich unter diesen Voraussetzungen in ein sozialtechnologisches Problem verwandeln, wobei die betreffenden Wertgesichtspunkte für diese Formulierung hpothethisch vorausgesetzt werden, wie das ja auch bei der Analyse der Erkenntnispraxis geschehen kann. Es läßt sich nämlich formulieren als Frage anch der Möglichkeit einer sozialen Ordnung, die bestimmten Anforderungen genügt, wobei dieser Anforderungen in den Kriterien (Leistungsmerkmalen) zum Ausdruck kommen, an denen sich die vergleichende Untersuchung orientiert. Da es bei solchen Vergleichen nicht um logische, sondern um reale Möglichkeitne geht, müssen die in Betracht kommenden Gesetzmäßigkeiten berücksichtigt werden. Und da es im konkreten Fall um die jeweils historischen Möglichkeiten geht, das heißt um die Realisierbarkeit in einem bestimmten Raum-Zeit-Gebiet, müssen die in diesem Gebiet vorliegenden tatsächlichen Bedingungen in die Analyse einbezogen werden.
Es ist selbstverständlich, daß auch die Anforderungen, die an eine adäquate Sozialordnung zu stellen sind, und die ihnen zugrundeliegenden Wertgesichtspunkte keineswegs der Diskussion zu entziehen sind. [24-5]
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. 
The charge levelled at the New Godless is that, with their rigorous reasoning, testing and experimentation, they are making a religion out of the scientific method. “It’s an all-purpose, wild-card smear,” retorts Dennett. “It’s the last refuge of the sceptic. When someone puts forward a scientific theory that they really don’t like, they just try to discredit it as ‘scientism’. But when it comes to facts, and explanations of facts, science is the only game in town.”
No argument can force us to accept the truth of any belief. But a valid deductive argument can force us to choose between the truth of its conclusion on the one hand and the falsity of its premises on the other. 
Every proof must proceed from premises; the proof as such, that is to say, the derivation from the premises, can therefore never finally settle the truth of any conclusion, but only show that the conclusion must be true provided the premises are true. [ch. 11, 260]
The political artist clamours, like Archimedes, for a place outside the social world on which he can take his stand, in order to lever it off its hinges. But such a place does not exist; and the social world must continue to function during any reconstruction. This is the simple reason why we must reform its institutions little by little, until we have more experience in social engineering.
This leads us to the more important second point, to the irrationalism which is inherent in radicalism. In all matters, we can only learn by trial and error, by making mistakes and improvements; we can never rely on inspiration, although inspirations may be most valuable as long as they can be checked by experience. [ch. 9, 181]
Such arguments in favour of Utopian engineering exhibit a prejudice which is as widely held as it is untenable, namely, the prejudice that social experiments must be on a ‘large scale’, that they must involve the whole of society if they are to be carried out under realistic conditions. But piecemeal social experiments can be carried out under realistic conditions, in the midst of society, in spite of being on a ‘small scale’, that is to say, without revolutionizing the whole of society. In fact, we are making such experiments all the time. The introduction of a new kind of life-insurance, of a new kind of taxation, of a new penal reform, are all social experiments which have their repercussions through the whole of society without remodelling society as a whole. Even a man who opens a new shop, or who reserves a ticket for the theatre, is carrying out a kind of social experiment on a small scale; and all our knowledge of social conditions is based on experience gained by making experiments of this kind. … But the kind of experiment from which we can learn most is the alteration of one social institution at a time. For only in this way can we learn how to fit institutions into the framework of other institutions, and how to adjust them so that they work according to our intentions. And only in this way can we make mistakes, and learn from our mistakes, without risking repercussions of a gravity that must endanger the will to future reforms. … But the piecemeal method permits repeated experiments and continuous readjustments. In fact, it might lead to the happy situation where politicians begin to look out for their own mistakes instead of trying to explain them away and to prove that they have always been right. This—and not Utopian planning or historical prophecy—would mean the introduction of scientific method into politics, since the whole secret of scientific method is a readiness to learn from mistakes. [ch. 9, 176-7]