Kant scholars have rarely addressed the notion of optimism as it was interpreted by the Königsbergian philosopher in the mid-18th century. The notion originates from Leibniz’s Theodicy and from debates over whether the actual world is the best of all possible worlds. The first of a two-part series, this article studies the historical context in which appeared Kant’s 1759 lecture advertisement leaflet entitled An Attempt at Some Reflections on Optimism. The study describes the requirements of the 1755 Berlin Academy of Sciences’ competition for a comparison of G. W. Leibniz’s and A. Pope’s systems and an assessment of optimism. Another focus is the philological difficulties of translating Pope’s proposition “Whatever is, is right” into the French language — which was part of the competition task. The author considers the ways the proposition was translated into the Russian and German languages. The article shows the contribution of Voltaire and his Poem on the Lisbon Disaster and Candide: or, Optimism to the post factum changes in the perception of the competition results and to the emergence of new shades of meaning in the concept of optimism. The Lisbon earthquake of 1755 had a profound effect on Europe and on the perception of optimism and of the idea that the actual world is the best of all possible worlds. However, Kant’s epistolary legacy leads one to the conclusion that the philosopher examined the problem in the framework of a polemic on Crusian philosophy. This article presents Crusius’s arguments against the theory that this is the best of all possible worlds and in favour of the theory that there are several good worlds. God’s choice of the actual world owes therefore to the freedom of contradiction (libertas contradictionis) and to the freedom of contrariety (libertas contrarietatis), which are eliminated in the teaching of optimism.