There's No Art To Find The Mind's Construction In The Face
Explain this line from Macbeth:"There's no art/ to find the mind's construction in the face."
When King Duncan speaks this line from act 1, scene 4 of Shakespeare's Macbeth, he has just been informed that the Thane of Cawdor has been executed. Malcolm tells the king that the men in charge of the execution have not returned from the task yet, but that he (Malcolm) talked to someone who saw Cawdor's execution. This messenger said that Cawdor admitted his crimes, deeply repented, and asked King Duncan's forgiveness. Then the messenger reported to Duncan that Cawdor died very well. At the end of Malcolm's speech, King Duncan responds:
There's no art to find the mind's construction in the face. He was a gentlemen on whom I built an absolute trust.
An art in this context means a creative skill. We use this word in several contexts. For example, there is an art and a science to teaching and practicing medicine. This word art also refers to magic arts, like mind reading or fortune-telling. What King Duncan means by this is that one cannot read another's mind by looking at his face. King Duncan had placed absolute trust in the Thane of Cawdor, therefore his betrayal took him completely by surprise.
The description of the Thane of Cawdor's betrayal comes in act 1, scene 2 when Ross tells the king that the Norwegian flag is flying in Fife, and he saw the Norwegian king leading an immense army and being assisted by the Thane of Cawdor.
The irony of King Duncan's statement about not being able to read someone's mind based on their face is that he will be betrayed to an even greater degree by Macbeth, whom he is also unable to read and in whom he placed absolute trust.
To understand the meaning of this line, it is important to consider its context. This line comes from Act I, Scene IV, and is spoken by King Duncan. Here, Duncan is speaking with his noblemen, including Macbeth, about the Thane of Cawdor and his treason. Specifically, Duncan is saying that he had no idea that Cawdor would turn out to be a traitor. After all, it is impossible ("there's no art") to know what a person is thinking ("the mind's construction") simply by looking at the face, because a person can hide his true intentions and feelings.
Looking deeper, this line is just as applicable to Macbeth as it is to Cawdor. In the previous scene, for example, Macbeth listened intently to the witches, who prophesied that he would become the next king of Scotland. This prompted to Macbeth to suddenly start thinking about murdering King Duncan. But, just like Cawdor, Macbeth hides these murderous thoughts. In this scene, Macbeth acts completely loyal and trustworthy to Duncan.
So, for the second time, Duncan is unable to read the "construction" of a person's mind. This time, it is Macbeth's mind, and Duncan is completely clueless about the impending murder.
This is a line that is spoken in Act I, Scene 4 by King Duncan. He is talking to Malcolm after Malcolm has reported to him that the Thane of Cawdor has been executed. What Duncan means by this is that there is no way to tell what a man is like -- what his character is -- by looking at his face.
When Duncan says "there is no art" he means "there is no way." When he refers to a "man's construction" he means the man's character.
What he is saying is that Cawdor basically fooled him -- he thought Cawdor was loyal but he turned out to be a traitor.
King Duncan makes this observation in act 1 sc. 4 when Malcolm reports that the Thane of Cawdor who betrayed the king has been put to death. King Duncan means to say that what is hidden in the mind of a man can never be understood by looking at his face. That is to say, the face is never a true index of the mind. The king believed the Thane of Cawdor to be very trustworthy, but he secretly helped the Norwegian king against Duncan.
However this piece of comment also becomes an example of irony. As Duncan says this, Macbeth enters with Banquo and others. Having gone through the previous scene--act 1 sc. 3--we know that Macbeth, Duncan's most admired and trusted general, is tempted, by his own ambition and the prophecies of the witches, to kill the good old king and usurp the throne. Duncan has declared Macbeth as the new Thane of Cawdor, but it is an irony that this time it is going to be a worse kind of betrayal. Truly the 'mind's construction' can never be known from the face.