Following is my response to the recent finding that Marlowe and Shakespeare co-authored the Henry VI plays and the anonymous play Edward III. I start with a discussion of chronology and a clue in The Taming of A Shrew indicating that Marlowe wrote II Henry VI. I continue with a brief description of the methodology behind the Stratfordians (University of Pennsylvania engineers working with a Shakespeare scholar) who made the finding. I then dispute their co-authorship theory by showing how Acts and Scenes they find to have been written by Shakespeare in II Henry VI and Edward III exhibit unique ties to Marlowe. I continue by disputing their claim that George Peele and William Shakespeare co-authored Titus Andronicus by demonstrating deep ties in the Shakespeare portions to Marlowe’s works.
Chronology and The Taming of A Shrew
Chronology is important. Marlowe received his M.A. from Cambridge University in 1587. There is general agreement that he wrote his two Tamburlaine plays in 1587, and Dido, Queen of Carthage by 1588. In my book, The Marlowe-Shakespeare Continuum, I present indications that Doctor Faustus was on stage by 1588, The Massacre at Paris and the poem Hero and Leander by 1590, Edward II by March 1591, and The Jew of Malta by 1591. According to this chronology, the works we associate with Marlowe were completed roughly two years before he died.
One touchstone I use to date plays is the anonymous comedy The Taming of A Shrew, which in some respects is similar to Shakespeare’s The Taming of the Shrew, and in other respects, different. Published in 1594, it is well known that A Shrew parodies Marlowe’s Tamburlaine plays, Dido, Queen of Carthage and Doctor Faustus. It’s really quite clever, too. There’s much quoting of Marlowe verbatim, but note the following changes: I Tamburlaine has, “A sacred vow to heaven and him I make,/ Confirming it with Ibis’ holy name.” A Shrew deflates this flowery rhetoric to “Father I swear by Ibis’ golden beak.” I mean, what kind of oath is that? And II Tamburlaine refers to “the snowy Apennines,” a mountain range in Italy. In A Shrew it’s “the snowy Apenis.” Modern editions of A Shrew change this to “Apennines.” Did they miss the joke? That pun would be particularly appropriate for a wedding.
I agree with Louis Ule’s theory that Marlowe penned The Taming of A Shrew as a self-parody for the wedding of his sister Margaret in June, 1590.  A Shrew is about a father trying to marry off three daughters, with one of them a shrewish woman called Katherine. Shakespeare pares this down to two daughters, and names the father Baptista, which evokes John the Baptist. At the time of Margaret’s wedding, Marlowe’s father, John, had three daughters of marriageable age to marry off, and Christopher Marlowe’s mother’s name was Katherine. We don’t know if she was shrewish, but we do know that although she died seven weeks after her husband and requested to be buried near him, her daughters buried her in an entirely different churchyard.
If I am correct, A Shrew parodies works Marlowe wrote before June, 1590, when his sister got married. Now, A Shrew parodies Marlowe’s epic poem by unnecessarily raising Hero and Leander twice, and naming Sestos, where the poem takes place, twenty times. I therefore disagree with the standard notion that Marlowe was working on it in 1593, around the same time Shakespeare was penning Venus and Adonis. There are so many similarities between these two poems, though, that it is obvious Shakespeare was closely familiar with Hero and Leander, which was still in manuscript. But then again, Shakespeare was closely familiar with all of Marlowe’s work.
There is one other play that A Shrew parodies: II Henry VI. According to my theory, the implication is that Marlowe wrote it. This dovetails with the recent finding that Marlowe was a co-author with Shakespeare of the Henry VI plays and the anonymous Edward III. Let’s talk about that.
University of Pennsylvania Research
An engineering professor from the University of Pennsylvania and two of his students, working together with a Shakespeare scholar, used Word Adjacency Networks based on function words such as “with,” “one,” “toward,” “and” “wherever.” The engineers developed an algorithm that counted word adjacencies, or how often and how closely different sets of function words appear to each other in a text. They provide this example:
In Shakespeare’s Hamlet, the First Folio version, within five words after the word “with,” appears the function word “and,” plus the word “one” occurs two times. This is recorded in the diagram, with an arrow between “with” and “and,” plus an arrow between “with” and “one” assigned the value “2.” The next function word is “one.” Five words after it appear “and” in addition to “one,” so they draw an arrow between “one” and “and,” plus an arrow from “one” back to itself. They did the same for Thomas Dekker’s Satiromastix, and found that the Word Adjacency Network was much less busy. To account for the function words occurring more frequently in the sample from Hamlet, they performed a normalization process. They then compared Word Adjacency Networks directly using Relative Entropy. Since the methodology is complicated and I cannot do it justice, please see the paper itself, cited in this footnote. 
With large sets of data, the engineers developed profiles for certain playwrights. Using them, they attributed scenes and acts from II Henry VI to Marlowe or Shakespeare. Overall, they gave Act I to Marlowe, and Acts II-V to Shakespeare, except that Scenes 4.3-4.8, the Jack Cade scenes, are too close to call. I have found that the Jack Cade scenes have numerous similarities to Thomas Nashe’s writing, but they can’t develop a profile for Nashe because of insufficient data, since they only considered plays.  Please note that they attributed every scene in Acts III and V to Shakespeare.
I earlier mentioned that chronology is important. This is because an author’s style can change over time. Marlowe’s ornate style in the Tamburlaine plays, written under the influence of Edmund Spenser’s The Faerie Queene, is quite different from the style of his Edward II. According to my analysis, by 1590 in The Taming of A Shrew, Marlowe was parodying his earlier, ornate style. Shakespeare’s style changed over time, too.
The distance between the writing of a play and its publication is also important: a play is a living document that can change over time. The Jew of Malta wasn’t published until 1632. How close is it to the original? We do not know. Half of the plays in Shakespeare’s 1623 First Folio had never been published before. How close are they to the originals? The 1608 quarto for King Lear was quite different than its First Folio version.
There’s a distinct possibility that John Florio edited the First Folio, adding unusual words that made it more erudite, and adding new sentences to the text. Yet the engineers lumped six Marlowe plays together, and lumped 28 Shakespeare plays together, no matter when they were written, using only the First Folio versions, in order to get their Big Data.
I would have been more interested in how the early versions of the Henry VI plays, Titus Andronicus and Richard III compared to Marlowe and separately to the Shakespeare plays penned 10-15 years later. But the engineers didn’t look at that.
II Henry VI
Now, a few words about my research and methodology. In my book The Marlowe-Shakespeare Continuum, my focus is on language and on setting down the myriad similarities in language and thought between the writing of Marlowe and “Shakespeare.” I ran language similarities through the Early English Books Online database, and only recorded similarities that were quite uncommon in English literature through 1700. I will here focus on Rare Scattered Word Clusters, which I particularly place stock in. These are a cluster of words extending over two or more lines that occur in two works in question, and no more than once elsewhere in the 32,000 works included in the Early English Books Online database at the time of my research. Not only are they extremely rare, but because they are scattered, they are less likely to be the result of copying, and more likely to be the result of a single mind.
Let’s return to the Henry VI plays. The engineers say II Henry VI, Act III, is all Shakespeare’s.
II Henry VI
By crying comfort from a hollow breast
Can chase away the first-conceived sound?
Hide not thy poison with such sugared words:
Lay not thy hands on me—forbear, I say!
Their touch affrights me as a serpent’s sting (3.2.43-8)
Dido, Queen of Carthage (Marlowe)
Breaking a spear upon his hollow breast,
Was with two winged serpents stung to death (2.1.165-6)
Rare Scattered Word Cluster: Hollow breast* near.100 serpent*
(* stands for endings such as "s," "ed," "ing," etc.)
The Rare Scattered Word Cluster results mean that out of the 32,000 works in the early literature database, only here and no more than once elsewhere do we find “hollow breast” within 100 words of “serpent.” Note also that in both instances serpent is followed by sting or stung.
Another example from Act III:
II Henry VI
King Henry. Ungentle Queen, to call him gentle Suffolk.
No more, I say! If thou dost plead for him…
[he tells Suffolk to leave the realm]
Come, Warwick; come, good Warwick, go with me. (3.3.294-5, 302)
Edward II (Marlowe)
Gaveston. On Mortimer; with whom, ungentle queen—
I say no more; judge you the rest, my lord…
Edward: Away, then! Touch me not. Come, Gaveston. (Sc. 4.149-50, 159)
Dido, Queen of Carthage (Marlowe)
Iarbus. Come, Dido, leave Ascanius! Let us walk!...
Ungentle queen, is this thy love to me?...
Dido. Something thou has deserved. Away, I say! (3.1.34, 36, 43)
Rare Scattered Word Cluster: Ungentle queen* near.200 come
The phrase “ungentle Queen” in and of itself is extremely uncommon. In Shakespeare’s Act III we see the Rare Scattered Word Cluster of “ungentle Queen” within 200 words of “come.” We find the same in Marlowe’s Edward II and Dido. Note the additional juxtaposition of “No more, I say,” or “I say no more,” plus in all three scenes, someone is being told to leave. It seems to me that the same mind appears to be at work in all three plays.
Act I contains what commentators have called a remembrance of university life:
II Henry VI
Now, lords, my choler being overblown
With walking once about the quadrangle, (1.3.155-6)
That’s understandable, it’s in the portion by Marlowe, who attended Cambridge. Harder to explain, smack dab in the middle of Shakespeare’s Act III, in a speech about Marlowe protagonist Dido Queen of Carthage, is:
II Henry VI
To sit and witch me, as Ascanius did,
When he to madding Dido would unfold
His father’s acts, commenced in burning Troy. (3.2.116-8)
The acts/commenced juxtaposition constitutes a thought pattern from Cambridge University. When a candidate for a degree at Cambridge successfully maintained a syllogistical dispute called “The Act,” he was said to “commence” in Arts or a Faculty. We hear the notion when Marlowe’s Doctor Faustus tells himself, “Having commenced, be a divine in show.”
Act V is also all Shakespeare’s, say the engineers. Yet in Scene 2 we hear:
II Henry VI
Thus war has given thee peace, for thou art still” (5.2.29)
Emrys Jones claims this is a remembrance from Marlowe’s yet-to-be published translation of the Roman poet Lucan’s Pharsalia, called Lucan’s First Book, because the war-peace antithesis is Marlowe’s, not Lucan’s. 
In Act V Scene 3, at the end of the play, Young Clifford laments his father’s death with:
II Henry VI
Young Clifford. O, let the vile world end,
And the premised flames of the last day
Knit earth and heaven together. (5.3.40-42)
II Tamburlaine (Marlowe)
Amyras. Meet heaven and earth, and here let all things end!
For earth hath spent the pride of all her fruit,
And heaven consumed his choicest
The two are strikingly similar.
III Henry VI
I find similar problems with the engineers’ attribution of III Henry VI Act I to Marlowe, the rest to Shakespeare (even though in Act I they only definitely attribute Scene 1 to Marlowe). But here I want to point out that it’s in Act I that we find the phrase:
II Henry VI
O tiger’s heart wrapped in a woman’s hide! (1.4.137)
Stratfordians have taken it as gospel truth that Robert Greene was raging against William Shakespeare when he parodied this line:
Groatsworth of Wit (Greene)
There is an upstart Crow, beautified with our feathers, that with his Tiger's heart wrapped in a Player's hide, supposes he is as well able to bombast out a blank verse as the best of you: and being an absolute Johannes factotum, is in his own conceit the only Shake-scene in a country.
Marlovians view it as far more likely that Greene’s target was the great actor Edward Alleyn. A Johannes factotum is a Jack of all Trades. Alleyn was an actor, musician, usurer, sharer, and possibly by then stage manager. It fits him. There’s the famous term “Shake-scene,” but Alleyn might have shaken the stage when he played, for example, the title role in Tamburlaine. As for bombasting out a blank verse, or being a playwright, Dolly Wraight and Daryl Pinksen proposed that Alleyn wrote the lost play Tambercam, and Peter Farey that Alleyn penned the anonymous play Faire Em. Indeed, the character of the Player in Greene’s Groatsworth of Wit has much more in common with Alleyn than with Shakespeare, according to Dr. Ros Barber. 
If Stratfordians acknowledge that Marlowe may have written the “tiger’s heart” speech, it supports the view that this passage isn’t about Shakespeare, in which case the first mention connecting Shakespeare with the stage isn’t until 1595, when he received payment with two other actors for a play performed December 1594. Remember also that it wasn’t until 1598 that a play was published with Shakespeare’s name on it.
As for the anonymous play Edward III, which Stratfordians claimed for Shakespeare a decade ago, the engineers give Act I to Marlowe, with Acts II and IV to Shakespeare; the authorship of other Acts is unclear. I proposed in my book that Marlowe wrote Edward III, then revised it at some point before it was registered in 1595. A.D. Wraight and other Marlovians maintain that Robert Greene referred to Marlowe writing at least Act I, where the Prince says “Ave Caesar” and stands next to a king:
Edward III (Anonymous)
Prince. As at the coronation of a king
The joyful clamours of a people are,
When Ave Caesar they pronounced aloud. (1.1.162-4)
Robert Greene wrote the following in a passage scholars agree is about actor Edward Alleyn:
Francesco’s Fortunes (Robert Greene), published in 1590, Julian calendar
If the Cobbler hath taught thee [Edmund Alleyn] to say, Ave Caesar, disdain not thy tutor [i.e., playwright], because thou pratest in a King’s chamber.
Marlowe was a cobbler’s son, but Greene uses Cobbler to refer to a historical incident from the days of Caesar Augustus. Alleyn acted the title roles in at least four of Marlowe’s plays. In other words, Marlowe was often Alleyn’s “tutor.” What’s especially important here is that Greene published this piece in 1590. Given the Julian calendar, that means some version of Edward III was on-stage by March 1591, and so, I argue, was Marlowe’s Edward II, which almost certainly was written before it. Also important is that Greene didn’t write “tutors,” i.e., multiple playwrights, but rather “tutor.”
I find Marlowe in Edward III where the engineers find Shakespeare. Compare Edward II’s soliloquy about death:
Edward II (Marlowe)
Baldock. Reduce we all our lessons unto this:
To die, sweet Spenser, therefore live we all;
Spencer, all live to die, and rise to fall. (Sc. 20.109-111)
Edward III (Anonymous)
Prince. Teach me an answer to this perilous time.
Audley. To die is all as common as to live:
The one in choice, the other holds in chase,
For from the instant we begin to live
We do pursue and hunt the time to die (4.4.133-137)
One has “teach,” the other “lessons.” The sentiments around the words “die” and “live” are similar. Edward III’s soliloquy is better, but to me it represents a natural progression in one playwright’s ability.
Again in Act IV, which the engineers find was by Shakespeare, here’s a Rare Scattered Word Cluster in two seemingly unrelated passages.
Edward III (Anonymous)
When we name a man,
His hand, his foot, his head, hath several strengths,
And, being all but one self instant strength,
Why, all this many, Audley, is but one,
And we can call it all but one man’s strength.
He that hath far to go tells it by miles:
If he should tell the steps it kills his heart; (4.4.52-8)
Hero and Leander (Marlowe)
And here and there her eyes through anger ranged.
And like a planet, moving several ways
At one self instant, she poor soul, assays,
Loving, not to love at all, and every part
Strove to resist the motions of her heart.
And hands so pure, so innocent, nay, such
As might have made heaven stoop to have a touch (li. 360-6)
Rare Scattered Word Cluster: Several* near.100 self instant* near.100 hand*
Note the juxtaposition of “several,” “one self instant,” “hand” and “heart” in Edward III and Marlowe’s Hero and Leander. Again, we appear to be seeing a single mind at work.
I am pleased that Stratfordians have found the hand of Marlowe in these plays, but I don’t think he’s a separate author from Shakespeare.
If everything I’ve written about so far was written by early 1591, did Marlowe twiddle his thumbs instead of writing between then and his supposed “death?” No, I propose that he penned Richard III, the anonymous play known as Woodstock, co-authored Titus Andronicus with George Peele, and wrote the poem Venus and Adonis, all before May 30th, 1593. Afterwards, I propose that he headed off to Italy for a while, absorbing fresh, new influences.
Titus Andronicus? But wait, the engineers find that George Peele wrote the first Act, and Shakespeare wrote the rest. Contemporary Stratfordians do NOT think Marlowe co-authored Titus Andronicus. The reader hears two hands, not three. Yet look at this Rare Scattered Word Cluster in Shakespeare’s portion, which occurs in these two works and nowhere else in the 32,000 pieces in the early literature database. Dido, Queen of Carthage:
Dido, Queen of Carthage (Marlowe)
Whose memory, like pale death’s stony mace,
Beats forth my senses from this troubled soul,
And makes Aeneas sink at Dido’s feet. (2.1.114-7)
Titus Andronicus, (Shakespeare portion) Quarto 1
(First Folio version replaces “souls” with “brains”)
And on the ragged stones beat forth our souls,
And make a mutual closure of our house. (K3v-K4r)
Rare Scattered Word Cluster: Make*/made near.100 beat* forth near.100 ston*
It’s a unique similarity in terms of thought.
Here’s another Rare Scattered Word Cluster:
In number more than are the quivering leaves
Of Ida’s forest, where your highness’ hounds
With open cry pursues the wounded stag (3.5.5-7)
The green leaves quiver with the cooling wind
And make a chequered shadow on the ground.
Under their sweet shade, Aaron, let us sit,
And, whilst the babbling echo mocks the hounds (2.3.14-17)
Rare Scattered Word Cluster Leaf*/leaves near.100 quiver* near.100 hound*
A quivering leaf is common enough, but nowhere else in the literature database is it found within one hundred words of hounds.
There are more amazing similarities where those came from, as I report in The Marlowe-Shakespeare Continuum, but for me this next find cements Marlowe’s involvement: We know that Marlowe got hold of a manuscript of The Faerie Queene and lifted whole phrases from it in his Tamburlaine plays. Hence, The Faerie Queene has: “To comfort me in my distressed plight,” while I Tamburlaine has: “Ah, shepherd, pity my distressed plight.”
If Titus Andronicus had copied Tamburlaine, that would be one thing, but Titus Andronicus returns instead to the source of Tamburlaine’s line in The Faerie Queene for: “And rather comfort his distressed plight.” To recap:
The Faerie Queene (Spenser)
To comfort me in my distressed plight (3.5.35)
I Tamburlaine (Marlowe)
Ah, shepherd, pity my distressed plight (1.2.7)
Titus Andronicus (Shakespeare portion)
And rather comfort his distressed plight (4.4.32)
The Faerie Queene Books I-III are 606 pages long and contain 18,081 lines (Slide 56) (Click again). The chances are MINISCULE that two separate authors would remember the same line from Spenser’s epic poem.
If scholars give the “Shakespeare” portion of Titus Andronicus to Marlowe, however, it becomes extremely difficult to argue that Shakespeare and Marlowe were two separate authors. See “The Trapped Fox Approach” here.
 Louis Ule, Christopher Marlowe (1564-1607). A Biography (New York: Carlton Press Corp., 1995), 27-32, 106-13, 173-80.
 Santiago Segarra, Mark Eisen, Gabriel Egan, and Alejandro Ribeiro, “Attributing the Authorship of the Henry VI Plays by Word Adjacency,” Shakespeare Quarterly 67 (2016): 232-256.
 See the first edition only of The Marlowe-Shakespeare Continuum, 94-102.
 Emrys Jones, The Origins of Shakespeare (Oxford: Clarendon Press, 1977), 273.
 Peter Farey, “The Batillus, the Player, and the Upstart Crow,” The Marlowe Society Research Journal 6 (2009): 1-9; A. D. Wraight, Christopher Marlowe and Edward Alleyn, 218; Daryl Pinksen, “Was Robert Greene’s ‘Upstart Crow’ the Actor Edward Alleyn?” The Marlowe Society Research Journal 6 (2009): 5-6; and Ros Barber, “Writing Marlowe as Writing Shakespeare: Exploring Biographical Fictions,” Ph.D. dissertation, University of Sussex, 2010, 95-6. http://rosbarber.com/wp-content/uploads/2012/01/RBarber-DPhil-Thesis-Chapter-5.pdf.