Although the principal subject of this paper is Ben Jonson's second tragedy, Catiline His Conspiracy (1611), a good deal of what I have to say is equally applicable to his earlier and somewhat more ambitious Sejanus His Fall (1603). The two plays are alike in many ways. For one thing, neither of them has ever been popular. Even among professed admirers, very few have been willing to praise them as highly as Jonson thought they deserved to be praised, and fewer still have seen any genuine tragedy in them. In fact, most criticism, favorable as well as unfavorable, has centered on such interesting but essentially peripheral matters as Jonson's use of the Senecan ghost and chorus (in Catiline), his portrayal of character, his reconstruction of the Roman scene, and, of course, his rhetoric. Discussions of Jonson's plots have scarcely gone beyond the problem of identifying his sources, and almost no one has touched upon the question of whether any real importance attaches to the use he made of those sources. This would not be particularly surprising, perhaps, if we were dealing with some competent journeyman, like Thomas Heywood for example, whose selection and use of sources is a matter of mainly academic interest; but in Jonson we have a playwright who not only aimed at something more than a popularly successful play but also set unusually great store by authenticity of fable—or “truth of argument,” as he called it—where tragedy was concerned (Works, IV, 350). His manipulation of material, therefore, especially at points where the disagreement of authoritative sources about a major issue forced him to make a choice, becomes a matter of considerable interest. It is certainly of interest to the historian, for it shows the sort of interpretation of history an intelligent and well-informed classical student of the seventeenth century might reasonably hold. My point, however, is that it is also a matter of literary interest. It can be shown, I think, that Jonson's ordering of his fable, rightly understood, gives the clue to why and how he expected these plays to be judged as tragedies rather than merely as serious history plays. In other words, it lets one see the conception of tragic drama that he worked by.