Some believe Joseph Smith dictated these lengthy quotations either by revelation or a prodigious feat of memory, without looking at a Bible. After all, his wife Emma testified in 1879 that Joseph “had neither manuscript nor book to read from” while he dictated the Book of Mormon. And several witnesses to the translation said Joseph dictated with his head in a hat.
A rival view is that when Joseph and Oliver encountered lengthy quotations from the “brass plates,” they copied from the King James Bible as a shortcut. They may have felt there was nothing wrong with this so long as Joseph examined the King James text and corrected its errors. When Emma denied that Joseph had used a book or manuscript, she may have meant only to deny the persistent rumor that he had plagiarized a novel. Or she may have just fibbed. She certainly told other lies, such as that Joseph had never practiced polygamy and never quarreled with her, or that he hadn’t forbidden her to view the plates but she’d never felt curious enough to peek.
How can we resolve this question? Possibly we could look for evidence in the original handwritten Book of Mormon manuscript. Certain kinds of scribal errors are characteristic of visual copying; others characteristic of dictation. Unfortunately much of the original Book of Mormon manuscript has been lost, and I don’t have ready access to the remainder. I leave that task to some future researcher.
What I do have access to are lots of manuscript revelations. And when I looked at how quotations are handled in these documents, I found something telling: sometimes the original dictated texts use placeholders or partial quotations later to be expanded into lengthy quotations copied from the Book of Mormon or Bible. It appears that Joseph and his scribes were indeed comfortable using this shortcut.
Below I outline four examples from revelations dictated in 1829 and 1830, close to when the Book of Mormon was translated.
Example #1: D&C 4:6
The original handwritten manuscript for D&C 4 is not extant, but we do have two different published versions. The revelation was first published in the 1833 Book of Commandments and then revised for the 1835 Doctrine and Covenants.
Verse 6 originally read, “Remember temperance, patience, humility, diligence, &c.” The revised text reads, “Remember faith, virtue, knowledge, temperance, patience, brotherly kindness, godliness, charity, humility, diligence.”
It appears that when Joseph first dictated this verse, he assembled a partial list of virtues meant to evoke New Testament passages such as Galatians 5:22–23 and 2 Peter 1:5–7. Perhaps forgetting the exact New Testament verbiage, he used the placeholder “&c.” (etcetera) to refer the reader back to the relevant biblical passages. In revising the verse for the 1835 D&C, he removed the placeholder and borrowed from 2 Peter 1:5–7 to expand the list of virtues.
Example #2: D&C 20:37
The earliest manuscript of D&C 20 is found in the journal of Zebedee Coltrin. It gives the following text for verse 37: “And again by way of commandment to the church concerning the manner of Baptism[:] Book of Mormon Page 576.”
The first edition of the Book of Mormon was not versified, so references were given by page number. “Page 576” is Moroni 6 in modern LDS editions. “Book of Mormon Page 576” was placeholder text indicating that a quotation should be inserted from the Book of Mormon. Thus in the 1833 Book of Commandments (24:29–30) the placeholder is replaced with text copied (with slight changes) from Moroni 6:2–3:
And again, by way of commandment to the church, concerning the matter of baptism; Behold whosoever humbleth himself before God and desireth to be baptized, and comes forth with a broken heart and a contrite spirit, and witnesseth unto the church, that they have truly repented of all their sins and are willing to take upon them the name of Christ, having a determination to serve him unto the end, and truly manifest by their works that they have received the Spirit of Christ unto the remission of their sins, then shall they be received unto baptism into the church of Christ.
Example #3: D&C 20:75–79
Another, similar example appears later in the same manuscript revelation. Here is the original text for D&C 20:75–76: “& it is expedient that the Church meet together often to partake of bread & wine in remembrance of the Lord Jesus & the Elder or Priest shall minister it & after this manner shall he do[:] Book of Mormon Page 175.”
“Page 175” was a scribal error; the correct page number was 575. In modern LDS editions, this is chapters 4 and 5 of Moroni. I won’t give the entire revised text, but suffice to say that for the 1833 Book of Commandments (24:55–59), the placeholder text “Book of Mormon Page 175” was replaced with a lengthy quote copied (again with slight changes) from Moroni 4 and 5.
Example #4: D&C 27:15
D&C 27:15 is available in manuscript form on page 36 of the Book of Commandments and Revelations. The manuscript text reads, “Wherefore lift up your hearts & rejoice & Gird up your loins & be faithful untill I come.” Although Joseph may not have intended this as a reference to Ephesians 6:13–17 when he first dictated the revelation, he certainly took it as one when he revised the text for the 1835 Doctrine and Covenants (50:3). There we find the passage expanded with a lengthy, slightly modified version of the Ephesians passage:
wherefore lift up your hearts and rejoice, and gird up your loins, and take upon you my whole armor, that ye may be able to withstand the evil day, having done all ye may be able to stand. Stand, therefore, having your loins girt about with truth; having on the breastplate of righteousness; and your feet shod with the preparation of the gospel of peace which I have sent mine angels to commit unto you, taking the shield of faith wherewith ye shall be able to quench all the fiery darts of the wicked; and take the helmet of salvation, and the sword of my Spirit, which I will pour out upon you, and my word which I reveal unto you, and be agreed as touching all things whatsoever ye ask of me, and be faithful until I come, and ye shall be caught up that where I am ye shall be also.
My analysis here does not support the view that Joseph Smith was always able or willing to dictate extended quotations from the Bible without referring to the text. Even if he was capable of doing so, he and his scribes seem sometimes to have opted for a shortcut. They may have found working with a source text more convenient or interesting than unaided dictation.
If Joseph and his scribes consulted a Bible to insert scriptural quotations into his revelations, one can certainly imagine them using a similar method in composing the Book of Mormon. Joseph may have marked up a King James Bible and instructed a scribe to copy from it, or he may have read aloud from the Bible while a scribe took dictation.
Update 4/16/2015 4:00 PM: An earlier version of this post erroneously asserted that all portions of the original Book of Mormon manuscript containing chapter-length Bible quotations have been lost. I’m grateful to Stanford Carmack for correcting me on this point.
 “Emma Smith Bidamon Interview with Joseph Smith III, February 1879,” in Early Mormon Documents, edited by Dan Vogel, 5 Vols. (Salt Lake City: Signature Books, 1996–2003), 1:542. (Hereafter cited as EMD.)
 See the accounts collected in John W. Welch, “The Miraculous Translation of the Book of Mormon,” in Opening the Heavens: Accounts of Divine Manifestations, 1820–1844, edited by John W. Welch and Erick B. Carlson (Provo, Utah: Brigham Young University Press, 2005), 123–28.
 “Emma Smith Bidamon Interview,” in EMD 1:535, 539, 542. Emma was curious enough about the plates to require a rebuke in D&C 25:4: “Murmur not because of the things which thou hast not seen, for they are withheld from thee and from the world, which is wisdom in me in a time to come.” One resident of the Smiths’ neighborhood even told a newspaperman in 1831 that Emma had sneaked a peek into the box where the plates were hidden, with the consequence that a portion of the plates had permanently disappeared. “James Gordon Bennett Account,” in EMD 3:282–83, 289.
 Royal Skousen, “Book of Mormon Manuscripts,” Encyclopedia of Mormonism, edited by Daniel H. Ludlow (New York: Macmillan, 1992), 185–86. http://contentdm.lib.byu.edu/cdm/compoundobject/collection/EoM/id/4391/show/5544
 H. Michael Marquardt, Joseph Smith’s 1828–1843 Revelations (Maitland, Fl.: Xulon Press, 2013), Kindle ed., Chapter 2.
 Ibid., Chapter 24.
 Ibid., Chapter 29