Polonius blames love for Hamlet's madness and resolves to inform Claudius and Gertrude.
Each version includes lines and entire scenes missing from the others.
The play's structure and depth of characterisation have inspired much critical scrutiny.
Shakespeare may also have drawn on an earlier Elizabethan play known today as the Ur-Hamlet, though some scholars believe Shakespeare wrote the Ur-Hamlet, later revising it to create the version of Hamlet we now have.
He almost certainly wrote his version of the title role for his fellow actor, Richard Burbage, the leading tragedian of Shakespeare's time.