Quote by Jean-Baptiste Say
Some writers maintain arithmetic to be only the only sure guide in political economy; for my part, I see so many detestable systems built upon arithmetical statements, that I am rather inclined to regard that science as the instrument of national calamity.
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Summary
This quote suggests that the speaker disagrees with the idea that arithmetic is the sole reliable method in the field of political economy. Rather than viewing arithmetic as a trustworthy guide, the speaker argues that many flawed economic systems have been created based on arithmetical statements. Therefore, they consider arithmetic to be a potentially destructive tool that could lead to national disasters or calamities. The quote implies skepticism towards relying solely on mathematical calculations without considering other factors or aspects of political economy.