DAVINA: Ralph, this first line of the soliloquy is a great example of why Shakespeare is far and away the most quoted writer in the English language. Listen to this: “If it were done when 'tis done, then 'twere well it were done quickly”.

RALPH: For one the thing, it succinctly lays out the first point in Macbeth’s soliloquy – that they would gladly kill Duncan right now, if only they could be sure that there would be no lingering repercussions to come back and haunt them.

DAVINA: And the wording has an impressive poetic effect. Note the string of monosyllabic words, “If it were done when 'tis done then 'twere well it were done”; and also the repetition, “it were done”, “it is done”, “it were well”, “it were done”.

RALPH:  Macbeth then elaborates on this point using several linked metaphors. He begins,“If the assassination could trammel up the consequence, and catch with his surcease, success.”

DAVINA: To “trammel up” has two meanings, and Shakespeare uses both of them. You trammel up a horse by tying a strap between a fore leg and a hind leg. This restricts the horse so it cannot wander off at night. Macbeth is saying, “If only they could trammel up, or constrain, the consequences of the assassination.”

RALPH: A trammel is also a type of fish trap. That’s where the word trammel comes from, the latin words for three meshes, tri- macula. Two sides of the trap funnel the fish into a third mesh where it is caught. Using this second sense, Macbeth says, “If the assassination could trammel up the crown, or catch it like a fish in a net”.

DAVINA: Surcease means the same as cease; it’s the end of something. In this case, he’s referring to the end of Duncan’s life. The Macbeths’ “success” comes from Duncan’s “surcease” – a nice bit of wordplay.

RALPH: So the meaning of the phrase is: if only they could constrain the consequences while catching the crown, this would be the be-all and the end-all – this would be all there is to it. “The be-all and end-all” – one of hundreds of expressions invented by Shakespeare which we hear all the time.

DAVINA: So, if the Macbeths could be sure they wouldn’t face any consequences they’d kill Duncan as soon as possible, and “here, upon this bank and shoal of time, they would jump the life to come.” 

RALPH: A bank or shoal is a shallow part of the ocean, like a fishing bank or a sand bar. When a ship “crosses the bar” to enter port, it’s taking a risk by crossing an obstacle. So, in this speech, bank or shoal is a metaphor for a hazard. Note that this ocean metaphor links to the use of trammel as a fish trap.

DAVINA: Whereas a sand bank is located in a place — in this case, the ocean — the obstacle faced by the Macbeths is located in time; it’s a “bank and shoal of time”.

RALPH: If the Macbeth’s could constrain the consequences, they would risk getting over their obstacle, they “would jump the life to come”. The word “jump” refers to horse riding; one takes a risk in jumping over an obstacle. This riding metaphor links back to the sense of trammel used in reference to horses.