In his judicial restraint philosophy, Frankfurter was strongly influenced by his close friend and mentor Oliver Wendell Holmes, Jr., who had taken a firm stand during his tenure on the bench against the doctrine of "economic due process". Frankfurter revered Justice Holmes, often citing Holmes in his opinions. In practice, this meant Frankfurter was generally willing to uphold the actions of those branches against constitutional challenges so long as they did not "shock the conscience." Frankfurter was particularly well known as a scholar of civil procedure.