Sonnet XXXIX

O! how thy worth with manners may I sing,
When thou art all the better part of me?
What can mine own praise to mine own self bring?
And what is't but mine own when I praise thee?
Even for this, let us divided live,
And our dear love lose name of single one,
That by this separation I may give
That due to thee which thou deserv'st alone.
O absence! what a torment wouldst thou prove,
Were it not thy sour leisure gave sweet leave,
To entertain the time with thoughts of love,
Which time and thoughts so sweetly doth deceive,
   And that thou teachest how to make one twain,
   By praising him here who doth hence remain.

This reads like a deferred reply to the proposition of sonnet 36 :
Let me confess that we two must be twain,
Although our undivided loves are one,
a sonnet which may be read as if it were spoken by the young man (although written by his advocate). The poet now gives his considered response, prefacing it with the observation that, as things now stand, any praise he makes of the young man will appear to be praise of himself. So, for that reason alone, he is prepared to admit that they should live separate lives, as the young man suggests. He would then be free to praise his love unstintingly without appearing to heap upon himself a mass of self-praise.

But this leaves him with the further thought that he will have to endure the bitterness and torment of absence, which, in thought, he tries to alleviate by imagining that he will be able to contemplate his beloved at a distance, and entertain the time with thoughts of love, so that the separation becomes a joining together, and the poet singly becomes united with the youth. It is no doubt a poor substitute for being in the young man's company, but for the time being he sees no other remedy and it is the only way to make the sourness of absence sweeter.

The 1609 Quarto Version

O how thy worth with manners may I ſinge,
When thou art all the better part of me?
What can mine owne praiſe to mine owne ſelfe bring;
And what is't but mine owne when I praiſe thee,
Euen for this,let vs deuided liue,
And our deare loue looſe name of ſingle one,
That by this ſeperation I may giue:
That due to thee which thou deſeru'ſt alone:
Oh abſence what a torment wouldſt thou proue,
Were it not thy ſoure leiſure gaue ſweet leaue,
To entertaine the time with thoughts of loue,
VVhich time and thoughts ſo ſweetly doſt deceiue.
   And that thou teacheſt how to make one twaine,
   By praiſing him here who doth hence remaine.

Commentary

1. O! how thy worth with manners may I sing,
with manners = appropriately, without offending propriety, in accordance with social conventions.
sing = praise (through my poems). A poet was a singer of verse, according to the classical tradition.
2. When thou art all the better part of me?
the better part - this calls to mind the phrase 'my better half', meaning 'my spouse, partner', a phrase which was current at the time. Shakespeare uses it in a manner appropriate to the interchange of souls in CE:
It is thyself, mine own self's better part;
Mine eye's clear eye, my dear heart's dearer heart CE.III.2.61-2.
It could also mean 'soul, spiritual part' as opposed to 'body' which was the meaner part. Cf. Sonn 74:
The earth can have but earth, which is his due;
My spirit is thine, the better part of me.
3. What can mine own praise to mine own self bring?
What advantage is there in praising myself? With the added suggestions: a.) from the line above, that praise of myself is praise of my better part, i.e. you, and my praise of you is of little worth; b.) self praise is always empty.
4. And what is't but mine own when I praise thee?
what is't but mine own = is it any different from what was mine already? Since you are my better part, any praise of you is praise of myself.
5. Even for this, let us divided live,
Even for this = for these reasons that I have just enumerated. let us divided live = let us live separate lives, without openly acknowledging our love for each other. It is uncertain what this phrase actually would imply in the relationship between the speaker and the beloved, assuming that such a relationship did exist, and that it was not entirely fictional. It hardly seems likely that they were living together under one roof, enjoying an open homosexual relationship, for the mores of the time would scarcely have permitted it. One imagines that a metaphorical separation is being proposed, just as the 'living together' was already metaphorical. Within the community of friends among whom this undivided love between the pair had its birth, the language of 'true love' was both acceptable and desirable, and probably was greeted with a plethora of reactions, including admiration and devoted praise, a clamouring for more and more invention, as well as sardonic laughter and bawdy ribaldry. Despite the serious tone of the sonnets, there is also a strong flavour of satire in many of them, and the courtly pastoral tradition of Marlowe's
Come live with me and be my love,
with its light hearted frivolity, happily co-exists with the agonised heart-wrenching of the Petrarchan tradition.

Assuming that the sonnets were publicised among his circle of friends, we might well ask whether or not this declaration 'Even for this let us divided live' would in fact make any difference to the relationship which had been established between poet and lover. If Shakespeare were for example a frequent visitor to Essex House or Lord Southampton's dwelling on the Strand, where perhaps he had met the youth of the sonnets, was he intending to cease visiting those places, so that he might maintain the separation from his beloved?

These are questions which we cannot answer, although I think it is important to continue to ask them, for it thus forces upon ourselves the consideration of the circumstances which might have given rise to this and other sonnets in the first place, and encourages us to put ourselves as close as possible to the heart of the writer, rather than maintaining the vicarious pleasure of distance which reading another person's verse can so easily create within us.

6. And our dear love lose name of single one,
dear = precious, highly valued.
single one = a love that is united in two hearts which have become one.
7. That by this separation I may give
As a result of this voluntary separation I may give.
8. That due to thee which thou deserv'st alone.
That due to thee = that which is your due i.e. praise of your worth.
thou deserv'st alone = you alone (and no one else) deserve to receive; or, you deserve to receive when not chained (figuratively) to me.
9. O absence! what a torment wouldst thou prove,
The speaker now considers the consequences of the proposed separation.
absence - sc. of you from me and of me from you. Separation.
10. Were it not thy sour leisure gave sweet leave,
sour leisure = bitter time (to me) in which you entertain yourself with me absent.
leave = permission. The roughness of the metre perhaps suggests the pain and bitterness of separation.
11. To entertain the time with thoughts of love,
To entertain the time = to fill up the time, to provide entertainment for myself in order to kill time.
12. Which time and thoughts so sweetly doth deceive,
doth - the Q reading is dost which several editors retain. 'dost' is the second person singular of the verb 'do', so it requires that the subject 'which' refers back to 'O absence' in line 9, giving effectively 'O absence, thou which (who) time and thoughts so sweetly dost deceive'. This is an awkward reading, because it seems to distort the flow of the sense, and because it is not absence that beguiles the time but the thoughts of love which absence permits to the estranged person. The most obvious antecedent which the sense seems to demand is the closest one, namely love or thoughts of love. SB and other modern editors emend to doth.
13. And that thou teachest how to make one twain,
And that thou - i.e. absence of line 9. This reverts back to the distant antecedent absence, which did not fit the sense in the previous line. Despite the 'and', which half implies that the same subject which sweetly deceives time and thoughts also teaches how to make one twain, it is easier on the understanding to accept a different referent for each line. It is also entirely consonant with standard Shakespearian practice to weave different meanings and references into the same sentence.
to make one twain = to make a single person into a pair, or partners. Although twain also has the meaning of 'separate', so a slightly jarring note is also added as an undertone.
14. By praising him here who doth hence remain.
here = in this place where I am; in this poem.
(him)... who doth hence remain = the beloved, who remains far off.