He grew to believe that the Austrian School had deviated from Carl Menger's original vision of an entirely subjective economics. To Lachmann, Austrian Theory was to be characterized as an evolutionary, or "genetic-causal", approach against the stresses of equilibrium and perfect found in mainstream Neoclassical economics.
Lachmann's "fundamentalist Austrianism" was rare—few living Austrian economists saw their work as departing from the mainstream. His work stressed all the points he saw as distinctive from that mainstream: Economic subjectivism, uncertainty, the business cycle, methodological individualism, alternative cost and "market process".
His work was highly influential upon the later "American branch" of the Austrian School.