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.
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.