Our definition, again, affords a rough rather than an exact separation from comedy. The two species cannot, indeed, be absolutely distinguished. In the theatre to-day there are many plays which one hesitates to classify as either tragedy or comedy. And there have always been, even in the Greek theatre, classes of plays recognized as neither the one nor the other. Again, a play presenting various persons and incidents is necessarily complex in material and emotional effect, and may mingle suffering and ruin with happiness and success, so that whether its main effect is tragic or comic may depend on its point of view or its general tone. The divisions of tragedy and comedy are neither mutually exclusive, nor are they together inclusive of all drama. Theoretically, there is perhaps ground for doubting whether other divisions might not be established more essential and more comprehensive. Comedy in particular comprises plays differing so widely in every respect that almost no common characteristics can be found. Yet tragedy and comedy have long been, and still are, accepted as the main divisions of the drama. The very names of the other forms, "tragicomedy," "_Schauspiel_" "emotional drama," "social drama," "_drame_," or merely "play," by their lack of distinctiveness, testify to the significance of the division of dramatic action and effects into the two classes, tragic and comic. From merely a theoretical point of view, indeed, we may recognize that a dramatic action, through its brevity and its stage presentation, if for no other reasons, has a suitability for these effects not possessed by other forms of literature. But the importance and definition of the two forms, and especially that of tragedy, depend less on theory than on historical origins and development.