The transition between competing paradigms cannot be made a step at a time, forced by logic and neutral experience. Like the gestalt switch, it must occur all at once (though not necessarily in an instant) or not at all.

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.

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.

All significant breakthroughs are break -“withs” old ways of thinking.

"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.

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

Every important idea in science sounds strange at first.