since being unable to view it all at once, we lose the effect of a single whole; for instance, suppose a creature a thousand miles long.
As then creatures and other organic structures must have a certain magnitude and yet be easily taken in by the eye, so too with plots: they must have length but must be easily taken in by the memory.
The limit of length considered in relation to competitions and production [Note] before an audience does not concern this treatise. Had it been the rule to produce a hundred tragedies, the performance would have been regulated by the water clock, as it is said they did once in other days.
But as for the natural limit of the action, the longer the better as far as magnitude goes, provided it can all be grasped at once. To give a simple definition: the magnitude which admits of a change from bad fortune to good or from good fortune to bad, in a sequence of events which follow one another either inevitably or according to probability, that is the proper limit.
A plot does not have unity, as some people think, simply because it deals with a single hero. Many and indeed innumerable things happen to an individual, some of which do not go to make up any unity, and similarly an individual is concerned in many actions which do not combine into a single piece of action.