… is from page 135 of Michael Polanyi’s deep 1958 volume, Personal Knowledge  (original emphases):
Scientific discovery reveals new knowledge, but the new vision which accompanies it is not knowledge. It is less than knowledge, for it is a guess; but it is more than knowledge, for it is a foreknowledge of things yet unknown, and at present perhaps inconceivable. Our vision of the general nature of things is our guide for the interpretation of all future experience. Such guidance is indispensable. Theories of the scientific method which try to explain the establishment of scientific truth by any purely objective formal procedure are doomed to failure. Any process of enquiry unguided by intellectual passions would inevitably spread out into a desert of trivialities. Our vision of reality, to which our sense of scientific beauty responds, must suggest to us the kind of questions that it should be reasonable and interesting to explore.
Sometime during the Spring of 1981, having just become (through Hayek) fascinated with Michael Polanyi ‘s work, I was chatting with Fritz Machlup  about Polanyi. Machlup knew both Michael and Michael’s older his brother Karl . Machlup said with a knowing smile, “Karl thought with his heart; Michael thought with his head.”