The text below is the one printed in the first edition of the Boston Evening Transcript on Friday 25 November 1864, the day the letter reached Mrs Bixby. It is the only authority for the wording. No manuscript, draft, copy or letter-book entry has ever been found, and the "facsimiles" sold from 1891 onward were traced in pencil and inked over on the wrong paper, as the autograph dealer Charles Hamilton showed in Great Forgers and Famous Fakes (1980, pp. 29 to 37). Basler reprinted the Transcript text in his edition, The Collected Works of Abraham Lincoln (1953), volume VIII, pages 116 to 117 (cited below as CW VIII, 116 to 117), with the note that "there is no reason to question the authenticity of the text of the letter which appeared in the Transcript and other contemporary sources." Every stylistic analysis, including ours, therefore rests on the 139 words as the Transcript's compositor set them in type.
The facts in the letter were wrong. Two of Lydia Bixby's sons were killed (Charles, 3 May 1863; Oliver, 30 July 1864); one deserted, one was honourably discharged, and one was captured and either deserted to the enemy or died in prison (Basler, CW VIII, 117 n.). The error was Schouler's, and it has no bearing on who composed the sentences.
The paper trail from Boston to the White House is complete and was printed by Schouler himself in 1868 (History of Massachusetts in the Civil War, I, 576 to 578) and re-examined in the National Archives by Bullard in 1946 (pp. 14 to 26). On 24 September 1864 Schouler reported to Governor Andrew on the case of Otis Newhall of Lynn, a father of five soldiers who had asked for one son's discharge, and added "a word in regard to a still more remarkable case": a widow who had shown him "five letters from five different company commanders, and each letter informed the poor woman of the death of one of her sons." Andrew forwarded the papers to the War Department with the sentence that set the letter in motion: "This is a case so remarkable, that I really wish a letter might be written her by the President of the United States, taking notice of a noble mother of five dead heroes so well deserved." The War Department received the papers on 26 and 27 September; Major Thomas M. Vincent, of the Adjutant General's office in Washington, asked Schouler for names and regiments on 1 October; Schouler replied on 12 October; Colonel Samuel Breck of the same office summarised the two cases for Stanton, the Secretary of War, on 28 October, ending "Governor Andrew desires that a letter may be written Mrs. Bixby by the President." The file was signed out to Stanton that day. On 5 November Schouler called on Lincoln in Washington and "passed an agreeable half hour with him" (Schouler's report for 1864, p. 606); nothing records that the Bixby case came up. The letter is dated Monday 21 November. Schouler placed it in Mrs Bixby's hands on the morning of Friday 25 November, and the Transcript had it in type the same day (Bullard, pp. 26, 50 to 51). How the letter travelled from Washington to Schouler's office is not documented.
Two things in this trail matter for authorship. The request reached Lincoln through the Secretary of War with a governor's explicit wish that the President write, which is the kind of request that came to the President personally rather than to the mail clerks. And the letter left no trace in the White House: no draft in Lincoln's hand, no draft in Hay's hand, no copy. Both facts are consistent with either author, as section 3 explains.