The unities were invented by Aristotle in his famous incomplete work the "Poetics", and they work as follows:
- The unity of action: the play should have one main story which it follows from start to finish. There should be no subplots (other stories worked into the first one).
- The unity of place: the stage should represent only one location, and not require scene changes to shift from place to place.
- The unity of time: the action of a play should take place fluidly, without jumping forward. This is sometimes interpreted as meaning that a play must take place within a time scale of 24 hours.
Sophocles' "Oedipus Rex", which Aristotle believed was the perfect tragedy (though there is some scholarly debate about exactly why) follows these unities. The play takes place in one location, requires no scene changes, and follows a single plot (though, of course, it doesn't seem like that to begin with) - that of Oedipus' realisation of who he is.
"King Lear" of course, does not follow the unities - at all. It has a multiplicity of scenes in a variety of locations from the palace to Dover beach, it takes place over a longer time than 24 hours (difficult to know precisely how much longer, but certainly longer) and - of course - it has two plots: the one which follows Lear's family and the one which follows Gloucester.
Hope this helps!
One of the most difficult plays to analyze with reference to the minor unities of time and place is the tragedy of King Lear. Unlike most of Shakespeare's plays there is not even a hint as to time,not a single reference being made to it throughout the whole play. Critics have estimated that the play itself covers ten days, with an interval between Act I, scene 2, and Act I, scenes 3 and 4, of something less than a fortnight, with the possibility of an interval of a day or two between Act IV, scene 2, and Act IV, scene 3. This would make the longest period, including intervals, that can be allowed for this play, one month. This can be but a matter of interpretation and inference, however, for there is nothing which can give definite proof of it. To the average reader the time seems much longer. Such intensity of action, such multiplicity of events seems to demand many months or even years. As to place, that, too, is uncertain. We are quickly trans ported from palace to palace, from castle to heath, from the British to the French camp. But we scarcely realize it. Never do we stop to ask, " Now just where is this palace, camp, or heath situated?" We do not know, and we do not care. Evidently Shakespeare himself thought it of little consequence, since he made no effort to reveal it to us. In King Lear, again, we have a somewhat complicated plot, but essential unity is maintained.