Grant Hardy discusses how Joseph may have translated the Book of Mormon.
Grant Hardy, "The Book of Mormon Translation," BYU Studies 60, no. 3 (2021): 203-9
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He obviously did not know the language of the plates—reformed Egyptian (Morm. 9:32). His own education was limited, and the first rudimentary decipherment of any form of ancient Egyptian by scholars had happened just a few years earlier. So when Joseph spoke of “translating,” he was not using the word in its ordinary sense, whereby someone who knows the source language perceives the meaning and then formulates corresponding expressions in the target language. Some Latter-day Saints believe that the seer stone allowed Joseph to bypass the first step in such a way that the meaning of the golden plates’ text was revealed to him in a nonverbal or preverbal form, which he then put into his own words. Other Latter-day Saints think that when he looked at the seer stone, he could see English letters and words, which he read aloud to his scribes. This means that there was a pre-existing translation, which he could access through the stone. (John Gilbert, the non-LDS typesetter for the first edition, put it this way: “The question might be asked here whether Jo or the spectacles was the translator?”)
Either way, when Joseph “translated,” he was rarely looking at the characters on the plates, which were usually either on the table covered in cloth or hidden elsewhere in the house or vicinity. At the same time, however, the process was not as straightforward as ordinary reading, since David Whitmer reported that if Joseph was not spiritually in tune (as when he had some sort of argument with his wife Emma), the device did not work. In addition, Oliver Cowdery once attempted to translate and failed—though it is uncertain whether he had tried to use the seer stone (D&C 9).
Eyewitnesses to the translation process believed that Joseph was reading a pre-existing text. According to Martin Harris, “By aid of the seer stone, sentences would appear and were read by the Prophet . . . , and when finished he would say, ‘Written,’ and if correctly written, that sentence would disappear and another appear in its place, but if not written correctly it remained until corrected,” with Joseph occasionally spelling out difficult words or names. Other witnesses, including Emma Smith, Joseph Knight Sr., David Whitmer, and John Whitmer, gave similar reports. These witnesses did not look into the seer stone themselves, and there is no record of Joseph ever explaining the translation process, so their descriptions are presumably based on their own observations of Joseph at work. Nevertheless, an examination of the text of the Book of Mormon, particularly the original manuscript, may provide additional evidence.
In comparing these accounts to the original manuscript (of which 28 percent is extant), linguist Royal Skousen proposed three theories of translation: “loose control,” in which ideas were revealed to Joseph and then put into his own language; “tight control,” where he saw specific words and read them to his scribes; and “iron-clad control,” in which his reading from the stone could not move forward if a scribe had made an uncorrected mistake. Most of the witnesses appear to have believed the last theory, though the presence of spelling and transcription errors in the original manuscript appears to disprove it. Clearly the dictation moved forward even when a few words were missed by the transcriber or when names were misspelled. (It is important to note that the three theories refer only to the translation process, not to the translation itself. The English Book of Mormon may be a rather free translation that was nevertheless revealed word for word. In fact, the presence of so many phrases from the King James Version, particularly from biblical texts written after 600 BC, argues strongly for it being a translation characterized by functional rather than formal equivalence.)
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