What is the relationship between main plot and subplot in King Lear?

The main plot and subplot in King Lear make the play
exceedingly complicated, especially since both old men are forced to leave their homes
and roam the countryside in different places. Added to this, Cordelia is far away in
France and Edgar is hiding out somewhere in the open country. Shakespeare shows a
boldness in the construction of this play and a disregard of the Aristotelian unities
that is unprecedented. All the characters are scattered in different places. Goneril and
Regan are given different domains, so they too are separated much of the time.
Meanwhile, Kent is a vagabond because he has been exiled by Lear. Oswald appears in
several different places. No one knows what happened to Lear's one hundred knights. The
Fool drops out of sight. Shakespeare must have had much confidence in himself and in his
audience, especially since he had to present all of this on a small stage with very
limited scenery and props.

Shakespeare may have felt he
needed a subplot because nothing much happens to Lear after he disowns his two daughters
and goes off on his own. Lear can do nothing to regain his power or to get revenge
against Goneril and Regan. There would have been, so to speak, "no second act."
Cordelia’s invasion from France has a deus ex machina quality about it. Shakespeare
devised the subplot to suggest that children turning against their parents was not an
isolated phenomenon but to dramatize what he believed was common in human nature. In
Lear’s case it was daughters, in Gloucester’s it was a son who thrust the older
generation out into the cold.

At that stage in his life
Shakespeare was becoming quite cynical about humanity, as he shows in his
Timon of Athens, for example. And here is a pertinent quote from
his Measure for Measure:

readability="17">

Friend hast thou
none,

For thine own bowels, which do call thee
sire,

The mere effusion of thy proper
loins,

Do curse the gout, serpigo, and the
rheum,

For ending thee no
sooner.

It should be noted
that Shakespeare is not only showing children against fathers but brother against
brother and sister against sister, even servant against master. In Act 4, Scene 2, the
Duke of Albany, thoroughly disgusted with his wife Goneril,
says:

If that
the heavens do not their visible spirits

Send quickly down
to tame these vile offences,

It will
come,

Humanity must perforce prey on
itself,

Like monsters of the
deep.