Now a whole is that which has a beginning, middle, and end. A beginning is that which is not itself necessarily after anything else, and which has naturally something else after it; an end is that which is naturally after something else, either as its necessary or usual consequent, and with nothing else after it; and a middle, that which is by nature after one thing, and also has another after it... A well constructed Plot, therefore, cannot either begin or end at any point one likes; beginning and end in it must be of the forms just described. Again: to be beautiful, a living creature, and every whole made up of parts, must not only present a certain order in its arrangement of parts, but also be of a certain definite magnitude.
--Aristotle, The Poetics
Path: Front Desk