… is from page viii of the 1936 English-language edition (translated by Alfred Stonier and Frederic Benham) of the Preface to the German Edition of Gottfried Haberler ’s classic 1933 book, The Theory of International Trade With Its Application to Commercial Policy  (footnote deleted):
Some readers will doubtless be surprised that the policy of Free Trade, which is in glaring contrast to the policy actually adopted by nearly every country in the world, should be advocated in this book. The universality of Protection inspires an instinctive distrust of a theory whose conclusions are nowhere accepted in practice. Can a policy which is rejected with such unanimity be correct?
But this is not an argument. It would be absurd to expect economic science to reverse the verdict of its analysis, based upon accepted judgments of value, just because in practice it is consistently ignored. Nobody would dream of asking medical science to change its findings just because everybody followed some custom which it had pronounced injurious to health.
Nevertheless it cannot be denied that the principles stated in this book as ‘economically correct’ have hardly ever been completely applied. The disagreeable task of having to declare current practice misguided, thereby provoking the accusation of unfruitful doctrinarianism, is one which the present volume shares with most scientific writings on international trade. Economists are nearly unanimous in favour of a liberal trade policy as are Governments in favour of the contrary.