Shakespeare took the material for his tragedy from the same source on which he drew for all his English histories—Holinshed's Chronicle to wit. In this case Holinshed, at no time a trustworthy historian, simply reproduced a passage of Hector Boece's Scotorum Historiæ. Macdonwald's rebellion and Sweno's Viking invasion are fables; Banquo and Fleance, as founders of the race of Stuart, are inventions of the chroniclers. There was a blood-feud between the house of Duncan and the house of Macbeth. Lady Macbeth, whose real name was Gruoch, was the grand-daughter of a king who had been killed by Malcolm II., Duncan's grandfather. Her first husband had been burnt in his castle with fifty friends. Her only brother was killed by Malcolm's order. Macbeth's father also, Finlegh or Finley, had been killed in a contest with Malcolm. Therefore they both had the right to a blood-revenge on Duncan. Nor did Macbeth sin against the laws of hospitality in taking Duncan's life. He attacked and killed him in the open field. It is further to be observed that by the Scottish laws of succession he had a better right to the throne than Duncan. After having seized the throne he ruled firmly and justly. There is a quite adequate psychological basis for the real facts of the year 1040, though it is much simpler than that underlying the imaginary events of Holinshed's Chronicle, which form the subject of the tragedy.
Shakespeare on the whole follows Holinshed with great exactitude, but diverges from him in one or two particulars. According to the Chronicle, Banquo was accessory to the murder of Duncan; Shakespeare alters this in order to give King James a progenitor of unblemished reputation. Instead of using the account of the murder which is given in the Chronicle, Shakespeare takes and applies to Duncan's case all the particulars of the murder of King Duffe, Lady Macbeth's grandfather, as committed by the captain of the castle of Forres, who "being the more kindled in wrath by the words of his wife, determined to follow her advice in the execution of so heinous an act." It is hardly necessary to remark that the finest parts of the drama, such as the appearance of Banquo's ghost and Lady Macbeth's sleep-walking scene, are due to Shakespeare alone.
Some sensation was made in the year 1778 by the discovery of the manuscript of The Witch, a play by Shakespeare's contemporary Middleton, containing in their entirety two songs which are only indicated in Macbeth by the quotation of their first lines. These are "Come away, come away" (iii. 5), and "Black spirits, &c." (iv. I). A very idle dispute arose as to whether Shakespeare had here made use of Middleton or Middleton of Shakespeare. The latter is certainly the more probable assumption, if we must assume either to have borrowed from the other. It is likely enough, however, that single lines of the lesser poet have here and there been interpolated in the witch scenes of Shakespeare's text as contained in the Folio edition.
Shakespeare has employed in the treatment of this subject a style that suits it—vehement to violence, compressed to congestion—figures treading upon each other's heels, while general philosophic reflections occur but rarely. It is a style eminently fitted to express and to awaken terror; its tone is not altered, but only softened, even in the painfully touching conversation between Lady Macduff and her little son. It is sustained throughout with only one break—the excellent burlesque monologue of the Porter.
The play centres entirely round the two chief characters, Macbeth and Lady Macbeth; in their minds the essential action takes place. The other personages are only outlined.
The Witches' song, with which the tragedy opens, ends with that admirable line, in which ugliness and beauty are confounded:—
"Fair is foul, and foul is fair."
And it is significant that Macbeth, who has not heard this refrain, recalls it in his very first speech:—
"So foul and fair a day I have not seen."
It seems as if these words were ringing in his ears; and this foreshadows the mysterious bond between him and the Witches. Many of these delicate consonances and contrasts may be noted in the speeches of this tragedy.