The axiom ‘A’ is equal to ‘A’ appears on one hand to be the point of departure for all our knowledge, on the other hand the point of departure for all the errors in our knowledge. To make use of the axiom of ‘A’ is equal to ‘A’ with impunity is possible only within certain limits. When quantitative changes in ‘A’ are negligible for the task at hand then we can presume that ‘A’ is equal to ‘A’. … To determine at the right moment the critical point where quantity changes into quality is one of the most important and difficult tasks in all the spheres of knowledge …

— Leon Trotsky, The ABC of Materialist Dialectics (1939)