Physical concepts are free creations of the human mind, and are not, however it may seem, uniquely determined by the external world.
conceptsquotes
The view is often defended that sciences should be built up on clear and sharply defined basal concepts. In actual fact no science, not even the most exact, begins with such definitions. The true beginning of scientific activity consists rather in describing phenomena and then in proceeding to group, classify and correlate them.
The principle of contradiction establishes merely the agreement of concepts, but does not itself produce concepts.
Words are but symbols for the relations of things to one another and to us; nowhere do they touch upon absolute truth…. Through words and concepts we shall never reach beyond the wall off relations, to some sort of fabulous primal ground of things.
Our understanding is a faculty of concepts, i.e., a discursive understanding, for which it must of course be contingent what and how different might be the particular that can be given to it in nature and brought under its concepts.
Philosophy is the discipline that involves creating concepts.
Nothing is more important for teaching us to understand the concepts we have than to construct fictitious ones.