Sonnet CLI

Love is too young to know what conscience is,
Yet who knows not conscience is born of love?
Then, gentle cheater, urge not my amiss,
Lest guilty of my faults thy sweet self prove:
For, thou betraying me, I do betray
My nobler part to my gross body's treason;
My soul doth tell my body that he may
Triumph in love; flesh stays no farther reason,
But rising at thy name doth point out thee,
As his triumphant prize. Proud of this pride,
He is contented thy poor drudge to be,
To stand in thy affairs, fall by thy side.
   No want of conscience hold it that I call
   Her love, for whose dear love I rise and fall.

The 1609 Quarto Version

LOue is too young to know what conſcience is,
Yet who knows not conſcience is borne of loue,
Then gentle cheater vrge not my amiſſe,
Leaſt guilty of my faults thy ſweet ſelfe proue.
For thou betraying me, I doe betray
My nobler part to my groſe bodies treaſon,
My ſoule doth tell my body that he may,
Triumph in loue,fleſh ſtaies no farther reaſon,
But ryſing at thy name doth point out thee,
As his triumphant prize,proud of this pride,
He is contented thy poore drudge to be
To ſtand in thy affaires,fall by thy ſide.
   No want of conſcience hold it that I call,
   Her loue,for whoſe dear loue I riſe and fall.

Commentary

1. Love is too young to know what conscience is,

Love = Cupid, usually depicted as a naked boy, the son of Venus. He was unaware of the pain his arrows caused. See sonnets 153 and 154. Also love in general terms, the experience of loving.
conscience - probably, in this line, an innate knowledge of right and wrong. Different meanings are established as the poem develops. KDJ suggests a hidden pun based on 'the prick of conscience' and 'the prick which has no conscience', from the Latin proverb penis erectus non habet conscientiam, 'a standing prick has no conscience', which may have been current at the time. (KDJ.p.418). Since the poem is mostly about male erection the hidden pun is probably intended, but I suspect it relies as much on 'the prick of conscience' and 'the prick of love' rather than the Latin proverb. Love was thought to be thorny and prickly because it caused so much pain, as well as bliss. Compare :
ROMEO Is love a tender thing? it is too rough,
Too rude, too boisterous, and it pricks like thorn.
MERCUTIO If love be rough with you, be rough with love;
Prick love for pricking, and you beat love down. RJ.I.4.25-8.

2. Yet who knows not conscience is born of love?

who knows not = who is unaware of the fact that, who does not know. The phrase has a hint of the opposite meaning, because of its similarity to who knows? = perhaps. It is possible that everyone is unaware, (since Cupid himself and those in love are blind).
conscience is born of love = love gives birth to conscience. Conscience comes into being because of the experience of love. A lot depends here on the interpretation of the word conscience. The locus classicus for its hallowed Christian meaning of an inner moral guide, as Shakespeare often seems to use it, is in the Tempest:
.............................But, for your conscience?
ANT. Ay, sir; where lies that? if 'twere a kibe,
'Twould put me to my slipper: but I feel not
This deity in my bosom: twenty consciences,
That stand 'twixt me and Milan, candied be they
And melt ere they molest! Tem.II.1.266-71.
Note: kibe = chilblain.
And also in :
Put thy sword up, traitor;
Who mak'st a show but dar'st not strike, thy conscience
Is so possessed with guilt: Tem.I.2.469-71.
The word occurs over 120 times in the plays, and its usual meaning is, as in the above extracts, the recognition of moral good and evil. But on other occasions it slips over into a more general sense, akin to the meaning of consciousness or awareness, as in this example from Hamlet.
Thus Conscience does make cowards of us all. Ham.III.1.83.

Nevertheless it seems that Shakespeare is deliberately punning in this sonnet on another sense based on a bawdy interpretation of con- as cunt, which allows the word to have the slang meaning of cuntscience, or knowledge of cunts. (An early spelling is given by OED as cunscience). Instances of punning on con- are found in the plays, and one gets the impression that Elizabethan audiences would have enjoyed the jokes, which were no doubt accompanied by obscene gestures. Examples are given below. In the first, from AWW, the clown offers to supply an answer that will fit any occasion. Below your duke to beneath your constable would be made to sound like 'below your dick to beneath your cunts-table', and would be accompanied by crude gestures. The Countess then shows that she is not above a bawdy joke herself, by suggesting that the answer is a monstrous penis. (The clown's clever answer for all occasions is O Lord, sir!). In the next example, which is in French, the English audience were expected to understand the puns. Katherine receives an English lesson in which the word for gown is pronounced as coun by Alice, which sounded probably like the French for 'cunt'. The word for pied, foot, probably sounded to Katherine like the French foutre 'to fuck', hence her exclamation that she would not pronounce such bad words before French gentlemen.Because of the more obvious sexual innuendoes in the rest of this sonnet, it is clear that conscience in this line, and in line 13 has an additional bawdy meaning which contributes more to the poem than the traditional meaning of 'this deity in my bosom'.  See the article by Dr. T. Merriam referred to above. Merriam.

COUNTESS. Have you, I say, an answer of such fitness for all questions?
CLOWN. From below your duke to beneath your constable, it will fit any question.
COUNTESS. It must be an answer of most monstrous size that must fit all demands.
CLOWN. But a trifle neither, in good faith, if the learned should speak truth of it: AWW.II.2.27-33.

KATHERINE. Ainsi dis-je; de elbow, de nick, et de sin. Commet appelez-vous le pied et la robe?
ALICE. De foot, madame; et de coun.
KATHERINE. De foot et de coun! O Seigneur Dieu! ce sont mots de son mauvais, corruptible, gros, et impudique, et non pour les dames d'honneur d'user: je ne voudrais prononcer ces mots devant les seigneurs de France pour tout le monde. Foh! le foot et le coun! H5.III.4.44-51.

3. Then, gentle cheater, urge not my amiss,

cheater - as the examples below show, the word was used in a sense which is now obsolete, a manager of the king's escheats, (OED.1) but it also has the more recognisable sense of one who swindles. An escheator was a sort of accountant and collector of dues, a financial manager, which is what is implied in the examples from Henry IV, although neither Falstaff nor Mistress Quickly, certainly not the latter, seem to have a clear idea of what is intended. In the final MWW example Falstaff deliberately chooses the financial meaning and then puns on it to suggest that he will work the post to his advantage. As Onions says (p.43), the word plays on the meaning of 'swindler, one who deals fraudulently'.
gentle cheater could therefore be 'one who manages me gently', or 'one who defrauds me but puts a pleasant gloss on it'. In the context of the playfulness of the poem the phrase has a tender ring to it, rather than accusatory, rather like tender churl in sonnet 12. So, given that Cupid was considered to be a mischievous cheat, it could be simply an expression of endearment and mean no more than 'dearest love'.
urge not = do not accuse me of being guilty of, do not press me about, do not incite me (with).
my amiss = my sin, error, failing, crime. There is much debate about what the sin might be, and opinions swing between two opposites. It could be the fault of being too randy and too demanding sexually, alternatively it could be that of being too cautious and shy, unable to satisfy his mistress's libidinous demands. The poem may be read with either sense, but lines 7-12 seem to lean more to the interpretation that the poet is accused of being too sexually demanding, especially as he is contented to be her drudge. It is impossible to know precisely what the fault was, and even if we were alive at the time and knew the participants it is doubtful if we could have access to the intimate knowledge that they shared and thereby answer the query.

There is a further difficulty with this line, in that the introductory Then which is equivalent to 'so, therefore,' implies that these two lines (3-4) are logically a continuation of the thought expressed in the previous line. Since we all know that conscience is born of love, he is saying, the beloved clearly has no right to accuse him of his amiss, whatever it might be. Yet even if we accept the bawdy meaning of conscience, it is unclear why the acquisition of it should free him from the charge of being too demanding, or not demanding enough, and why he can therefore say that his beloved is guilty of his fault, or of the self same fault.

FALSTAFF He's no swaggerer, hostess; a tame cheater, i' faith; you may stroke him as gently as a puppy greyhound: he'll not swagger with a Barbary hen, if her feathers turn back in any show of resistance.
Call him up, drawer.
[Exit First Drawer]
MISTRESS QUICKLY Cheater, call you him? I will bar no honest man my house, nor no cheater: but I do not love swaggering, by my troth; I am the worse, when one says swagger: feel, masters, how I shake; look you, I warrant you.
DOLL TEARSHEET So you do, hostess. 2H4.II.4.92-101.

MISTRESS QUICKLY No, Good Captain Pistol; not here, sweet captain.
DOLL TEARSHEET Captain! thou abominable damned cheater, art thou not ashamed to be called captain? 2H4.II.4.130-2.

FALSTAFF O, she did so course o'er my exteriors with such a greedy intention, that the appetite of her eye did seem to scorch me up like a burning-glass! Here's another letter to her: she bears the purse too; she is a region in Guiana, all gold and bounty. I will be cheater to them both, and they shall be exchequers to me; MWW.I.3.62-9.

4. Lest guilty of my faults thy sweet self prove:

You may turn out to be guilty of the very same faults you charge me with; or, you may turn out to be guilty of inciting me to commit the fault you accuse me of. prove = turn out to be.

5. For, thou betraying me, I do betray

For, thou betraying me = because your seduction of me causes me to etc. For betray as catch, entice, seduce, compare:
.........................................I will betray
Tawny finned fishes; my bended hook shall pierce
Their slimy jaws. AC.II.5.11-13.
These two lines (5-6) are explanatory of why she will turn out to be guilty of his 'amiss'. Taking betray in its normal sense of 'be a traitor to' the sense seems to be 'your example of betrayal of me sets the pattern for my body to be a traitor to my soul, handing it over to the physical dominion of lust'. betraying me may also refer to the mistress taking another lover, and it has been suggested that the poem implies that the speaker finds this sexually titillating. The tone of the other sonnets, where his pain over her refusal to love him is amply documented, seems to rule this out. betray is used in one other sonnet:
How many lambs might the stern wolf betray,
If like a lamb he could his looks translate!
How many gazers mightst thou lead away,
If thou wouldst use the strength of all thy state! 96
It deals with the youth's unfaithfulness and his 'amiss' of taking another love, possibly this same woman.

6. My nobler part to my gross body's treason;

My nobler part = my soul, the better part of me.
my gross body = my body, which is made of earth, and is heavy in comparison with the soul. Shakespeare uses gross to describe Falstaff:
One of them is well known, my gracious Lord, a gross fat man. 1H4.II.4.559. OED.8.c. also cites the word as descriptive of material things in comparison with the spiritual and ethereal, with this example:
1530 Rastell Bk. Purgat. ii. vi, The soule of man may use hys operacyon & properte wythout occupyenge of the grosse bodye.

7. My soul doth tell my body that he may

The line is either an amplification of I do betray my nobler part to my gross body's treason, or, which is more likely, it is descriptive of a continuation of the process. Thus: 1. You betray me (l.5). 2. I betray my soul by using the body's treasonable temptings (l.5,6). 3. My soul responds by giving my body the go ahead (l.7,8). 4. My body does not wait any longer, but rises to do you service (l.8,9).

8. Triumph in love; flesh stays no farther reason,

Triumph in love = be a conqueror in love. The imagery from here on is ostensibly military. Triumph, rising, triumphant, proud, pride, stand, and affairs could all be given meanings in connection with military service. However it does not disguise the fact that the metaphors, in so far as they are metaphors at all, are predominantly sexual.
flesh = the body, mentioned in the previous line, but evidently with special reference to the penis, from what follows.
stays no further reason = does not wait for any further argument or justification. reason puns on raising or rising.

9. But rising at thy name doth point out thee,

at thy name = at the mere mention of you.
doth point out thee = points to you, indicates you. 'Point' is often used in connection with the hand of a clock or watch, or a gnomon, which points out the hour, as in:
O gentlemen, the time of life is short!
To spend that shortness basely were too long,
If life did ride upon a dial's point,
Still ending at the arrival of an hour. 1H4.V.2.82-5.

My thoughts are minutes; and with sighs they jar
Their watches on unto mine eyes, the outward watch,
Whereto my finger, like a dial's point,
Is pointing still, in cleansing them from tears. R2.V.5.51-4.

Mercutio jokes on the apparent sexual imagery of a clock (or sundial):
'Tis no less, I tell you, for the bawdy hand of the
dial is now upon the prick of noon. RJ.II.4.108-9.
No doubt this line of the sonnet hints also at the similarity of point and prick.

10. As his triumphant prize. Proud of this pride,

triumphant prize = the reward of his conquest.
Proud of this pride = swollen with the thrill of his victory. The imagery is still military, but with heavy insinuations of sexual performance. 

11. He is contented thy poor drudge to be,

He = the body, flesh, the penis, your serving soldier.
thy poor drudge = your menial servant who performs tedious duties.

12. To stand in thy affairs, fall by thy side.

To stand in thy affairs = to stand to attention like a serving soldier when your needs demand it. With obvious bawdy innuendo, since affairs in this context can be stretched to mean 'sexual affairs', 'vagina'. Compare from Antony and Cleopatra:
Ant. The business she hath broached in the state cannot endure my absence.
Eno. And the business you have broached here cannot be without you; especially that of Cleopatra's, which wholly depends on your abode. AC.I.2.165-9.
'Business' in this extract is equivalent to 'affairs' in the sonnet, and Enobarbus puns additionally on 'whole' and 'hole'. (broach = begin, as in broaching or opening a barrel).
fall by thy side = fall in for duty at your side, in your army. But the image is still predominantly sexual, with 'fall' meaning 'lose my erection (after making love)', or 'flop into bed beside you'.

13. No want of conscience hold it that I call

No want = no lack, no absence of.
hold it = consider it, think it, hold it as your opinion.
that I call / Her love = that I address her as 'My love'; that I consider her to be my love.

14. Her love, for whose dear love I rise and fall.

The conclusion seems to be that love has taught him duty, the duty of service to his mistress, in that he obeys her every command (rises and falls), therefore he cannot be accused of lacking a conscience since he is so assiduous in his devotion, and so sexually active on her behalf.