The reproach of careless organization has become a commonplace in the criticism of the Ars Poetica. Some commentators have been satisfied with merely putting on a derogatory label. Others have tried transposing passages in order to reduce the work to a system. Others, with or without appeal to Horace's sources, have tried in various ways to discern or to reconstruct some plan underlying the alleged disorder. None, so far as can be discovered, have made a successful attempt to find the key to the argument in the mode and manner of its presentation.The aim of this paper is to suggest such a key; to show that the proposed key is valid for the interpretation of all Horace's work; and particularly to show that the proper application of the key reveals in the Ars that lucid and logical thought-structure that is a constant characteristic of the Horatian manner.Horace is a writer of one idiom only. His method in all his works is an essentially ‘lyrical’ method, whether he is working on lyrical material proper or on satire, epistle, or didactic verse. The seeming casualness of the Ars is a mannerism of the lyrical style. Everywhere in Horace a disarming informality appears on the surface. But closer reading reveals a lucid and closely patterned sequence of thought. Once the lyrical manner is understood, once the key to its interpretation is applied, Horace's typically clear logic, in ode, satire, or treatise stands revealed.