For nearly two centuries, scholars have debated whether some 325 lines in the 1602 quarto edition of Thomas Kyd’s play “The Spanish Tragedy” were, in fact, written by William Shakespeare.

Last year, the British scholar Brian Vickers used computer analysis to argue that the so-called Additional Passages were by Shakespeare, a claim hailed by some as the latest triumph of high-tech Elizabethan text mining.

But now, a professor at the University of Texas, says he has found something closer to definitive proof using a more old-fashioned method: analyzing Shakespeare’s messy handwriting.

In a terse four-page paper, to be published in the September issue of the journal Notes and Queries, Douglas Bruster argues that various idiosyncratic features of the Additional Passages — including some awkward lines that have struck some doubters as distinctly sub-Shakespearean — may be explained as print shop misreadings of Shakespeare’s penmanship.

“What we’ve got here isn’t bad writing, but bad handwriting,” Bruster said in a telephone interview.

Claiming Shakespeare authorship can be a perilous endeavor. In 1996, Donald Foster, a pioneer in computer-driven textual analysis, drew front-page headlines with his assertion that Shakespeare was the author of an obscure Elizabethan poem called “A Funeral Elegy,” only to quietly retract his argument six years later after analyses by Vickers and others linked it to a different author.

This time, editors of some prestigious scholarly editions are betting that Bruster’s cautiously methodical arguments, piled on top of previous work by Vickers and others, will make the attribution stick.

“We don’t have any absolute proof, but this is as close as you can get,” said Eric Rasmussen, a professor at the University of Nevada, Reno, and an editor, with Jonathan Bate, of the Royal Shakespeare Company’s edition of the complete Shakespeare.

Rasmussen and Bate are including “The Spanish Tragedy” in the Royal Shakespeare Company’s new edition of Shakespeare’s collaboratively authored plays, to be published in November. And Bruster plans to include the Additional Passages in his new edition of the Riverside Shakespeare (renamed the Bankside Shakespeare), coming in 2016.

Tiffany Stern, a professor of early modern drama at Oxford University and an advisory editor for the Arden Shakespeare, praised the empirical rigor of Bruster’s paper, but said that some new attributions were driven less by solid evidence than by publishers’ desire to offer “more Shakespeare” than their rivals.

“The arguments for ‘The Spanish Tragedy’ are better than for most” putative Shakespeare collaborations, Stern said. “But I think we’re going a bit Shakespeare-attribution crazy and shoving a lot of stuff in that maybe shouldn’t be there.”

Bruster was less persuaded by the linguistic parallels, which he calls merely “suggestive.” And so he turned to perhaps the most literal source of authority: Shakespeare’s own pen.

In his paper, Bruster identifies 24 broad spelling patterns — including shortened past tenses (like “blest” for “blessed”) and single medial consonants (like “sorow” instead of “sorrow”) — that occur both in the Additional Passages, for which no known manuscript survives, and the Shakespeare handwriting sample in the British Library. He also cites nine textual “corruptions” (like “creuie” instead of “creuic,” modernized as “crevice”) that he believes can be explained as misreadings of Shakespeare’s handwriting.

These irregularities, considered individually, are not necessarily unique to Shakespeare. But taken together, Bruster argues, they strongly suggest that the Additional Passages were set in type from pages written, in the most literal sense, by Shakespeare.

The debate’s gone on for almost 200 years: Did Shakespeare write a portion of the Thomas Kyd play “The Spanish Tragedy”? A recently completed old-fashioned handwriting analysis may be the closest attempt so far at a definitive answer.