“necessities of thought”

Concepts that have proven useful in ordering things easily achieve such an authority over us that we forget their earthly origins and accept them as unalterable givens.  Thus they come to be stamped as “necessities of thought,” “a priori givens,” etc.  The path of scientific advance is often made impassable for a long time through such errors.  For that reason, it is by no means an idle game if we become practiced in analyzing the long commonplace concepts and exhibiting those circumstances upon which their justification and usefulness depend, how they have grown up, individually, out of the givens of experience.  By this means, their all-too-great authority will be broken.  They will be removed if they cannot be properly legitimated, corrected if their correlation with given things be far too superfluous, replaced by others if a new system can be established that we prefer for whatever reason.

[Einstein 1916 in obituary notice for Ernst Mach]