Apart from the Preface serving as the introduction to Samuel Johnson's own edition of Shakespeare's collected works, readers must view it as a major critical statement regarding not only Shakespeare but writing in general. Indeed, the preface lays out principles upon which later commentators have based their evaluations of literature.

Johnson begins by citing what he views as the justification for granting an overriding importance to Shakespeare. Significantly, his statements about Shakespeare can be seen as the basis of a general theory of aesthetics. Shakespeare, put simply, has stood the test of time. The only way a dramatist can still hold the stage 150 years after his death is that there is something of value that transcends the local considerations and spirit of the time in which he wrote. Johnson is drawing his conclusion from the observation of fact. In effect, he argues that longevity is the only real test of greatness.

In accounting for this timeless quality, Johnson states that Shakespeare 's virtue is that he accurately conveys human nature, action, and speech—in short, that he holds up a mirror to mankind. This isn't to say that he by any means considers Shakespeare a "perfect" author. He dismisses various criticisms made by Dennis, Rymer, and Voltaire, but at the same time, he enumerates the faults that he sees in Shakespeare as well. Arguably the most significant of these faults is what Johnson sees as a lack of moral compass in Shakespeare's work:

His first defect may be that to which may be imputed most of the evil in books or in men. He sacrifices virtue to convenience, and is so much more careful to please than to instruct, that he seems to write without any moral purpose.

Johnson was a religious man, a devout member of the Established Church. In all his writings one feels this, but the strength of his admiration for Shakespeare must be seen in this context. In spite of this lack of evidence of morality in Shakespeare, Johnson still judges him highly.

Johnson regards Shakespeare as a genius—but a kind of rough genius, appearing at a time when the English nation was still in a somewhat "barbarous" state. This gives us an indication of how far forward the Enlightened eighteenth century believed it had progressed beyond the relatively primitive past of the the Elizabethan and Jacobean eras. Much of the rougher aspect of Shakespeare—for instance, the multiplicity of characters and the density of action in his plots—Johnson attributes to this style having been what the largely uneducated audiences of Elizabethan and Jacobean times wanted.

While pointing out aspects that he does consider genuine faults, Johnson dismisses as irrelevant those critics who have cited Shakespeare's not observing the "unities" of time and place as a defect. The rationale for such unities, which were held as dramaturgical ideals since classical antiquity, has always been that they create and preserve for the audience a sense of illusion, of verisimilitude. But, Johnson argues, the spectator knows from the start that he is in a theater, and it does not matter if one act takes place in Alexandria and the next in Rome, and so on.

These observations of Johnson's are important not only as a defense of Shakespeare but because Johnson is stating a general principle of modern aesthetics which we, today, take for granted. Indeed, the classical ideal of the unity of time and place is no longer the standard, either in theater or in more modern forms.

Much of the Preface also deals with the question of the accuracy of different editions of Shakespeare that Johnson has...