II, i, 61-9. Tanner says:Since Cassius first did whet me against Caesar,
I have not slept.
Between the acting of a dreadful thing
And the first motion, all the interim is
Like a phantasma, or a hideous dream:
The Genius and the mortal instruments
Are then in council; and the state of man,
Like to a little kingdom, suffers then
The nature of an insurrection.
Shakespearean tragedy takes place in and focuses on, exactly, the "interim" between the first "motion" (or prompting, or provocation, or incitement, or some stirring inclination) and "the acting of a dreadful thing." The "motion" may be started by an ambiguous ghost (Hamlet) or a scheming devil (Othello), or equivocating witches (Macbeth). The "dreadful thing" is always murder--albeit in very different circumstances. The period in between is experienced by the protagonist as, in different ways, "like a phantasma, or a hideous dream". And that "phantasma" is, among other things, the phantasmagoria of the conscience started, startled, into unprecedented activity. The experience takes all the tragic protagonists, in varying degrees, to the edge of madness. ... These are the parameters of Shakespeare's major tragedies. And that is what they are about
--.Tony Tanner, Prefaces to Shakespeare 493 (2010)
I think this is wonderful, although perhaps Tanner overdoes it. I don't suppose it describes Lear or Antony and Cleopatra (both certainly major) nor, ironically, Julius Caesar itself (perhaps not quite major). But it certainly describes the three plays he mentions.
The prefaces, by the way, are a rewarding as good as the best introductions to Shakespeare perhaps but appreciative and insightful all the same.