In Shakespeare’s time, much scientific and social inquiry was built on “ocular proof”—the philosophical belief that the human eye was the (almost) infallible judge of what was real and what was not. The play starts out with this question, in the form of the conversation between the night sentinels, Barnardo and Francisco, followed by Horatio and Marcellus, in which they seek proof of identity by voice responses--imperfect evidences. Their conversation immediately goes to the play’s crux—“What, has this thing appeared again tonight?” (“Horatio says ‘tis but our fantasy.”) The appearance of Hamlet’s father’s ghost is the first occasion of the theme of appearance vs. reality. Even though the guards have “seen” the ghost, it falls short of “ocular proof” because, when a “state” is in turmoil (and Denmark is, because the king has died), hallucinations from the devil can distort human perception; this theme continues to develop throughout Act I Scene ii, and of course Scene v. Another example of this theme is the seeming madness of Hamlet himself; he may be reported as doing mad things, such as appearing in Ophelia’s rooms improperly dressed and later, in stabbing her father though the arras (itself an example of appearance vs. reality, since Hamlet thought Claudius, not Polonius, was hiding there). Then there is the pair of “school chums”, Rosencrantz and Guildenstern, who “in appearance” are friends but “in reality” are spies for Claudius. There is one other thematic touch in Shakespeare’s use of the Horatio character himself. In appearance he is a real “character” with a personality, a development, etc.—all the features of a constructed dramatic character; but his real function is that of a “literary device”; scholars have often pointed out that he serves as a way for the audience to hear Hamlet’s thoughts, when he speaks to Horatio, so that we, the audience can see he is not really mad; in fact, “Horatio character” has actually become a term to describe such a literary device in drama. One last “appearance vs. reality” moment in the play: Ophelia’s madness and suicide follows the theme. That she was mad is supported by the detail that she appears in public “with her hair down around her ears” (an Elizabethan metonomy for aberrant behavior); that she committed suicide is open to question, since in the “appearance vs. illusion” theme, she could have fallen into the stream by accident.