Moritz Schlick Quote

The 'physical' does not mean any particular kind of reality, but a particular kind of denoting reality, namely a system of concepts in the natural sciences which is necessary for the cognition of reality. 'The physical' should not be interpreted wrongly as an attribute of one part of reality, but not of the other ; it is rather a word denoting a kind of conceptual construction, as, e.g., the markers 'geographical' or 'mathematical', which denote not any distinct properties of real things, but always merely a manner of presenting them by means of ideas..

p. 27 i. ; as cited in: Adam Schaff (1962). Introduction to semantics, p. 83 - Allgemeine Erkenntnislehre, 1925