IT IS TO THINKING, much more than to observation, that we owe the impressive accomplishments of our science. It is on the point of reshaping the face of the earth and the structure of our life. It will certainly be worthwhile to reflect a little on this process of thinking. What actually is it? How is it possible that it helps us to get to know something? How is it formed, which ways does it go in scientific research? And finally, the most important question: what is its value? Can we trust it, believe in its results, permit it to lead us through scientific thinking? Today, I would like to discuss briefly some of these weighty questions with you.