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“Felix, qui potuit rerum cognoscere causas” is verse 490 of Book 2 of the "Georgics" . It is literally translated as: “Fortunate who was able to know the causes of things”. Virgil may have had in mind the Roman philosopher Lucretius, of the Epicurean school.
Wikipedia contributors, "Felix qui potuit rerum cognoscere causas," Wikipedia, The Free Encyclopedia, http://en.wikipedia.org/wiki/Felix_qui_potuit_rerum_cognoscere_causasABOUT THE LATIN LANGUAGE