When the whole of a given subject cannot be got within the limits of presentation, is there any means of determining how much should be left for retrospect, and at what point the curtain ought to be raised? The principle would seem to be that slow and gradual processes, and especially separate lines of causation, should be left outside the frame of the picture, and that the curtain should be raised at the point where separate lines have converged, and where the crisis begins to move towards its solution with more or less rapidity and continuity. The ideas of rapidity and continuity may be conveniently summed up in the hackneyed and often misapplied term, unity of action. Though the unities of time and place are long ago exploded as binding principles--indeed, they never had any authority in English drama--yet it is true that a broken-backed action, whether in time or space, ought, so far as possible, to be avoided. An action with a gap of twenty years in it may be all very well in melodrama or romance, but scarcely in higher and more serious types of drama.[4] Especially is it to be desired that interest should be concentrated on one set of characters, and should not be frittered away on subsidiary or preliminary personages. Take, for instance, the case of _The Second Mrs. Tanqueray_. It would have been theoretically possible for Sir Arthur Pinero to have given us either (or both) of two preliminary scenes: he might have shown us the first Mrs. Tanqueray at home, and at the same time have introduced us more at large to the characters of Aubrey and Ellean; or he might have depicted for us one of the previous associations of Paula Ray--might perhaps have let us see her "keeping house" with Hugh Ardale. But either of these openings would have been disproportionate and superfluous. It would have excited, or tried to excite, our interest in something that was not the real theme of the play, and in characters which were to drop out before the real theme--the Aubrey-Paula marriage--was reached. Therefore the author, in all probability, never thought of beginning at either of these points. He passed instinctively to the point at which the two lines of causation converged, and from which the action could be carried continuously forward by one set of characters. He knew that we could learn in retrospect all that it was necessary for us to know of the first Mrs. Tanqueray, and that to introduce her in the flesh would be merely to lead the interest of the audience into a blind alley, and to break the back of his action. Again, in _His House in Order_ it may seem that the intrigue between Maurewarde and the immaculate Annabel, with its tragic conclusion, would have made a stirring introductory act. But to have presented such an act would have been to destroy the unity of the play, which centres in the character of Nina. Annabel is "another story"; and to have told, or rather shown us, more of it than was absolutely necessary, would have been to distract our attention from the real theme of the play, while at the same time fatally curtailing the all-too-brief time available for the working-out of that theme. There are cases, no doubt, when verbal exposition may advantageously be avoided by means of a dramatized "Prologue"--a single act, constituting a little drama in itself, and generally separated by a considerable space of time from the action proper. But this method is scarcely to be commended, except, as aforesaid, for purposes of melodrama and romance. A "Prologue" is for such plays as _The Prisoner of Zenda_ and _The Only Way_, not for such plays as _His House in Order_.