THOMAS KUHN

It is, I think, particularly in periods of acknowledged crisis that scientists have turned to philosophical analysis as a device for unlocking the riddles of their field. Scientists have not generally needed or wanted to be philosophers.

The crises of our time, it becomes increasingly clear, are the necessary impetus for the revolution now under way. And once we understand nature's transformative powers, we see that it is our powerful ally, not a force to feared our subdued.

Crisis alone is not enough. There must also be a basis, though it need be neither rational nor ultimately correct, for faith in the particular candidate chosen.

Normal science does not aim at novelties of fact or theory and, when successful, finds none.

Rather than being an interpreter, the scientist who embraces a new paradigm is like the man wearing inverting lenses.

Under normal conditions the research scientist is not an innovator but a solver of puzzles, and the puzzles upon which he concentrates are just those which he believes can be both stated and solved within the existing scientific tradition.

The historian of science may be tempted to exclaim that when paradigms change, the world itself changes with them.

Individuals who break through by inventing a new paradigm are almost always...either very young or very new to the field whose paradigm they change....These are the men who, being little committed by prior practice to the traditional rules of normal science, are particularly likely to see that those rules no longer define a playable game and to conceive another set that can replace them.

What a man sees depends on what he looks at and what his previous experience has taught him to see.

All crises begin with the blurring of a paradigm and the consequent loosening of the rules for normal research. .. Or finally, the case that will most concern us here, a crisis may end with the emergence of a new candidate for paradigm and with the ensuing battle over its acceptance.

What a man sees depends both upon what he looks at and also upon what his previous visual-conceptual experience has taught him to see.

Groups do not have experiences except insofar as all their members do. And there are no experiences... that all the members of a scientific community must share in the course of a [scientific] revolution. Revolutions should be described not in terms of group experience but in terms of the varied experiences of individual group members. Indeed, that variety itself turns out to play an essential role in the evolution of scientific knowledge.

As in political revolutions, so in paradigm choice--there is no standard higher than the assent of the relevant community. To discover how scientific revolutions are effected, we shall therefore have to examine not only the impact of nature and of logic, but also the techniques of persuasive argumentation effective within the quite special groups that constitute the community of scientists.

Philosophers of science have repeatedly demonstrated that more than one theoretical construction can always be placed upon a given collection of data.

Communication across the revolutionary divide is inevitably partial.

The historian of science may be tempted to claim that when paradigms change, the world itself changes with them. Led by a new paradigm, scientists adopt new instruments and look in new places. even more important, during revolutions, scientists see new and different things when looking with familiar instruments in places they have looked before. It is rather as if the professional community had been suddenly transported to another planet where familiar objects are seen in a different light and are joined by unfamiliar ones as well.

What chemists took from Dalton was not new experimental laws but a new way of practicing chemistry (he himself called it the 'new system of chemical philosophy'), and this proved so rapidly fruitful that only a few of the older chemists in France and Britain were able to resist it.

"Normal science" means research firmly based upon one or more past scientific achievements, achievements that some particular scientific community acknowledges for a time as supplying the foundation for its further practice.

To turn Karl [Popper]'s view on its head, it is precisely the abandonment of critical discourse that marks the transition of science. Once a field has made the transition, critical discourse recurs only at moments of crisis when the bases of the field are again in jeopardy. Only when they must choose between competing theories do scientists behave like philosophers.

The resolution of revolutions is selection by conflict within the scientific community of the fittest way to practice future science. The net result of a sequence of such revolutionary selections, separated by periods of normal research, is the wonderfully adapted set of instruments we call modern scientific knowledge.

Though the world does not change with a change of paradigm, the scientist afterward works in a different world... I am convinced that we must learn to make sense of statements that at least resemble these. What occurs during a scientific revolution is not fully reducible to a re-interpretation of individual and stable data. In the first place, the data are not unequivocally stable.

Political revolutions aim to change political institutions in ways that those institutions themselves prohibit. Their success therefore necessitates the partial relinquishment of one set of institutions in favor of another, and in the interim, society is not fully governed by institutions at all

Each paradigm will be shown to satisfy more or less the criteria that it dictates for itself and to fall short of a few of those dictated by its opponent.

Research under a paradigm must be a particularly effective way of inducing paradigm change.

In science novelty emerges only with difficulty, manifested by resistance, against a background provided by expectation.