Prologue (Greek πρόλογος prologos, from προ~, pro~ - fore~, and lógos, word), or prolog, is a prefatory piece of writing, usually composed to introduce a drama. The Greek prologos included the modern meaning of prologue, but was of wider significance, embracing any kind of preface, like the Latin praefatio. The prologue is usually in the beginning of a book.
In Attic Greek drama, a character in the play, as very often a deity, stood forward or appeared from a machine before the action of the play began, and made from the empty stage such statements necessary for the audience to hear so that they might appreciate the ensuing drama. It was the early Greek custom to dilate in great detail on everything that had led up to the play, the latter being itself, as a rule merely the catastrophe which had inevitably to ensue on the facts related in the prologue. The importance, therefore, of the prologue in Greek drama was very great; it sometimes almost took the place of a romance, to which, or to an episode in which, the play itself succeeded.
It is believed that the prologue in this form was practically the invention of Euripides, and with him, as has been said, it takes the place of an explanatory first act. This may help to modify the objection which criticism has often brought against the Greek prologue, as an impertinence, a useless growth prefixed to the play, and standing as a barrier between us and our enjoyment of it. The point precisely is that, to an Athenian audience, it was useful and pertinent, as supplying just what they needed to make the succeeding scenes intelligible. But it is difficult to accept the view that Euripides invented the plan of producing a god out of a machine to justify the action of deity upon man, because it is plain that he himself disliked this interference of the supernatural and did not believe in it. He seems, in such a typical prologue as that to the Hippolytus, to be accepting a conventional formula, and employing it, almost perversely, as a medium for his ironic rationalism.
Many of the existing Greek prologues may be later in date than the plays they illustrate, or may contain large interpolations. On the Latin stage the prologue was often more elaborate than it was in Athens, and in the careful composition of the poems which Plautus prefixes to his plays we see what importance he gave to this portion of the entertainment; sometimes, as in the preface to the Rudens, Plautus rises to the height of his genius in his adroit and romantic prologues, usually placed in the mouths of persons who make no appearance in the play itself.
The tradition of the ancients vividly affected our own early dramatists. Not only were the mystery plays and miracles of the Middle Ages begun by a homily, but when the drama in its modern sense was inaugurated in the reign of Elizabeth, the prologue came with it, directly adapted from the practice of Euripides and Terence. Sackville, Lord Buckhurst, prepared a sort of prologue in dumb show for his Gorboduc of 1562; and he also wrote a famous Induction, which is, practically, a prologue, to a miscellany of short romantic epics by diverse hands.
In the Elizabethan drama the prologue was completely useless, very far from being universally employed. In the plays of William Shakespeare, for instance, it is an artifice which the poet very rarely introduced, although we find it in Henry V and Romeo and Juliet. Sometimes the Elizabethan prologue was a highly elaborated poem; in 1603 a harbinger recited a sonnet on the stage, to prepare the audience for Thomas Heywood's A Woman Killed with Kindness. Often the prologue was a piece of blank verse, so obscure and complicated that it is difficult to know how its hearers contrived to follow it; such are the prologues of George Chapman.
Among Elizabethan prologues the most ingenious and interesting are those of Ben Jonson, who varied the form on every occasion. For instance, in The Poetaster (1602), Envy comes in as Prologue, and speaks a long copy of heroics, only to be turned off the stage by an armed figure, who states that he is the real prologue, and proceeds to spout more verses. Jonson's introductions were often recited by the stage-keeper, or manager. Francis Beaumont and John Fletcher seem to have almost wholly dispensed with prologues, and the form was far from being universal, until the Restoration, when it became de rigueur.