Definition of Metaphor: 

A metaphor is a figure of speech that describes one thing by comparing it to another that is different. Metaphors are composed of a tenor and a vehicle, with the tenor being the object described and the vehicle being the imagery used to describe it. When the tenor and vehicle are both explicitly mentioned, it is a direct metaphor; when one or the other is merely implied, the metaphor is indirect. Sometimes metaphors are brief, contained within a few phrases to create a striking sensory image or profound connection. At other times they can extend throughout an entire work or even an author’s entire body of work. One example of the latter is Shakespeare’s likening of the world to a stage, which can be seen in works like The Merchant of Venice, Macbeth, and, perhaps most famously, As You Like It. In this example, “life” is the tenor, and the imagery of the stage is the vehicle for the comparison. 

Examples of Metaphor in Literature:

“Life's but a walking shadow, a poor player
That struts and frets his hour upon the stage
And then is heard no more.”
—William Shakespeare’s Macbeth

“I hold the world but as the world, Gratiano;
A stage, where every man must play a part,
And mine a sad one.”
—William Shakespeare’s The Merchant of Venice

“All the world’s a stage, and all the men and women merely players.” 
—William Shakespeare’s As You Like It

The metaphor of “world as a stage” did not originate with Shakespeare but is a common concept in his plays, often reminding the audience that they are watching or reading a play in the first place. The concept also conveys the idea that humans are constantly performing for one another and exist within assigned roles in society, offering a potential critique that goes beyond just the literary works themselves. 

“I felt a Funeral, in my Brain,
And Mourners to and fro
Kept treading—treading—till it seemed
That Sense was breaking through—”
—Emily Dickinson’s “I Felt a Funeral, in My Brain”

The metaphor of a funeral in the brain conveys the sense that the poem is referring to the condition of the speaker’s mental state. By using the vehicle of a funeral, associated with death and mourning, Dickinson conveys the idea that a part of her brain is “dying,” signifying that the tenor is a descent into madness as “sense” tries to “break through.”

“My heart aches, and a drowsy numbness pains
My sense, as though of hemlock I had drunk,
Or emptied some dull opiate to the drains
One minute past, and Lethe-wards had sunk:”
—John Keats’s “Ode to a Nightingale”

This quatrain contains examples of both direct and indirect metaphor. The speaker’s condition of an aching heart’s “drowsy numbness” is compared directly to the state of having drunk “hemlock” or “some dull opiate to the drains.” This state of intoxication is compared to sinking “Lethe-wards.” This is an indirect metaphor, because “Lethe” is an allusion that points to the true vehicle of the metaphor—forgetfulness. (Lethe is the mythical Greek river of forgetfulness in the Underworld.)