I should take the passage thus.  At ‘Hold, sir,’ [omitted in Qq.] Albany holds the letter out towards Edmund for him to see, or possibly gives it to him.[279] The next line, with its ‘thou,’ is addressed to Edmund, whose ‘reciprocal vows’ are mentioned in the letter.  Goneril snatches at it to tear it up:  and Albany, who does not know whether Edmund ever saw the letter or not, says to her ‘I perceive you know it,’ the ‘you’ being emphatic (her very wish to tear it showed she knew what was in it).  She practically admits her knowledge, defies him, and goes out to kill herself.  He exclaims in horror at her, and, turning again to Edmund, asks if he knows it.  Edmund, who of course does not know it, refuses to answer (like Iago), not (like Iago) out of defiance, but from chivalry towards Goneril; and, having refused to answer this charge, he goes on to admit the charges brought against himself previously by Albany (82 f.) and Edgar (130 f.).  I should explain the change from ‘you’ to ‘thou’ in his speech by supposing that at first he is speaking to Albany and Edgar together.

7.  V. iii. 278.

Lear, looking at Kent, asks,

Who are you? 
Mine eyes are not o’ the best:  I’ll tell you straight.

Kent. If fortune brag of two she loved and hated (Qq. or),
One of them we behold.

Kent is not answering Lear, nor is he speaking of himself.  He is speaking of Lear.  The best interpretation is probably that of Malone, according to which Kent means, ’We see the man most hated by Fortune, whoever may be the man she has loved best’; and perhaps it is supported by the variation of the text in the Qq., though their texts are so bad in this scene that their support is worth little.  But it occurs to me as possible that the meaning is rather:  ’Did Fortune ever show the extremes both of her love and of her hatred to any other man as she has shown them to this man?’

8. The last lines.

Alb. Bear them from hence.  Our present business
Is general woe. [To Kent and Edgar] Friends of my
soul, you twain
Rule in this realm, and the gored state sustain.

Kent. I have a journey, sir, shortly to go;
My master calls me, I must not say no.

Alb. The weight of this sad time we must obey;
Speak what we feel, not what we ought to say. 
The oldest hath borne most:  we that are young
Shall never see so much, nor live so long.

So the Globe.  The stage-direction (right, of course) is Johnson’s.  The last four lines are given by the Ff. to Edgar, by the Qq. to Albany.  The Qq. read ‘have borne most.’

To whom ought the last four lines to be given, and what do they mean?  It is proper that the principal person should speak last, and this is in favour of Albany.  But in this scene at any rate the Ff., which give the speech to Edgar, have the better text (though Ff. 2, 3, 4, make Kent die after his two lines!); Kent has answered Albany, but Edgar has not; and the lines seem to be rather more appropriate to Edgar.  For the ’gentle reproof’ of Kent’s despondency (if this phrase of Halliwell’s is right) is like Edgar; and, although we have no reason to suppose that Albany was not young, there is nothing to prove his youth.