When thou shalt be disposed to set me light,
And place my merit in the eye of scorn,
Upon thy side, against myself I'll fight,
And prove thee virtuous, though thou art forsworn.
With mine own weakness being best acquainted,
Upon thy part I can set down a story
Of faults concealed, wherein I am attainted;
That thou in losing me shalt win much glory:
And I by this will be a gainer too;
For bending all my loving thoughts on thee,
The injuries that to myself I do,
Doing thee vantage, double-vantage me.
Such is my love, to thee I so belong,
That for thy right, myself will bear all wrong.
When you criticise me, I will agree with your criticisms, and support your virtue, even though you have betrayed me. Knowing my own faults, I can be so convincing when I describe them, that you will be vindicated. Even I will win, because my love for you is such that any gain to you, gains me even more. I care about you so much that to help you I will harm myself.
The key to a full understanding this sonnet is found in the words “gainer” and “vantage”. The speaker envisages an inevitable (i.e. “When”), vigorous and adversarial incident between the sonnet’s “I” and the addressee, “thou”. This conflict is established by the words “scorn”, “side”, “fight”, “losing”, “win”, “gainer”, “vantage” and “double-vantage”. At first sight the sonnet’s final couplet seems to confirm a subservience of the speaker to the addressee which was apparently established earlier in the sonnet and earlier in the sequence. In 1963 Martin Seymore-Smith said of this sonnet,  "Not only does Shakespeare intend to love to the bitter end, but also he proposes to demolish the edifice of his own ego by this process of identification with the Friend" and that if we do not understand this "we have little chance of understanding the Sonnets as a whole." However, such an interpretation has been shown to be simplistic and erroneous. Far from being a loser, the speaker becomes a covert winner by gaining the “double-vantage”. In 1924 T.G. Tucker noted that “double-vantage" is from tennis, and apparently means that I, your opponent, myself get “vantage” every time I thus yield it to you”. In 2009 Fred Blick established by detailed argument, based on historical research into the Real Tennis of Shakespeare’s time, that “double-vantage” meant a win i.e. two vantage points in succession after a score of deuce (reflected in the sonnet’s number 8 – 8) to win a “set”, just as it means today. The word “set” then also meant a bet or stake (see OED, v. B. trans., 14, and the Fool in King Lear, "Set less than thou throwest", presumably at dice, I, iv, 123). Tennis was in Shakespeare’s day almost always played as a gamble or “set”, hence the origin of the scoring call “game and set”. This casts a new light on the typically Shakespearean resonance of the words in line 1, “set me light” (bet against me at scornful odds) and line 6, “set down”. Fred Blick has also shown that after sonnet 88 the speaker of the sonnets becomes more critical of the addressee and less subservient to him. Sonnet 126, at the end of the Fair Youth sequence, finally condemns to mortality the “lovely boy” as a mere human, no more than an equal of the mortal speaker. Perceptive as to structure, Helen Vendler did note in 1997 that the "doubling vantage that is the theme of the sestet of 88 helps to organize the whole Sonnet", but extremely valuable as her comments are, she did not observe the existence of the important tennis metaphor nor its relevance to the whole sequence.