A witness is someone who has seen an event take place or who otherwise has knowledge of something from personal observation or experience. The Lord's policy is that "In the mouth of two or three witnesses shall every word be established." (2 Corinthians 13:1, Matt 18:16, Ether 5:4, D&C 6:28) And yet, many of the first events of the Restoration of the gospel in these latter days appear to have no witnesses. Joseph Smith was alone when he had his first vision of God and his Son. He was alone when he was visited by the angel Moroni. He went through great lengths to keep the plates that contained the record of the Nephites hidden from sight. How can we know that these events actually happened?
1. The first vision. Joseph went alone to the woods to pray. How can we know that this event took place? What witnesses besides Joseph Smith can we turn to?
When Joseph returned home after this incredible experience, his mother noticed he had no strength and asked him what the matter was. She was a witness that something unusual had happened. At the time he only told her that he was well, and that he had learned for himself that Presbyterianism was not true. This isn't incredibly convincing.
However, Joseph's family does serve as a witness to his character. When Joseph's religious family learned of the vision they believed him, while other ministers and religious people who did not know him as well did not. What does this tell us about Joseph as a person? He was honest. He was not given to telling lies; his family would have known that and would have been skeptical of his claims. But they believed him, and this tells us something.
2. Moroni's visit. Three years later, when Joseph was visited by Moroni, he was again the only witness. What other witnesses do we have?
The morning following Joseph's sleepless night, he attempted to work as normal, but both his father and his brother Alvin witnessed that something was wrong with him: he was pale and weak, and his father sent him back to the house. When Joseph told his father about the heavenly messenger, his father believed him and told him that it was of God. Again, Joseph's father, who knew him well, believed him and this is a witness that Joseph was by nature an honest person.
When Joseph told the rest of the family they also believed him. His mother tells, "I think that we presented the most peculiar aspect of any family that ever lived upon the earth, all seated in a circle, father, mother, sons, and daughters, listening in breathless anxiety to the religious teachings of a boy eighteen years of age who had never read the Bible through by course in his life." (History of Joseph Smith by His Mother, p 111.) They were witnesses that Joseph had received knowledge of many things of which he had not previously been aware.
3. The Golden Plates. In spite of the efforts Joseph went to in order to keep the plates hidden from sight, there are many witnesses to their existence.
First, there is again Joseph's family. They were witnesses of Joseph's actions in procuring the plates, finding and paying for a locked chest to contain them, hiding them from people who would steal them, and of the long hours spent in translating them.
Those who tried to steal the plates are, in their own way, witnesses of their existence. The lengths that they went through in their attempts to get them are proof that they firmly believed in the plates' existence.
Martin Harris, Emma Smith, and Oliver Cowdrey, who served as scribes as Joseph translated the writing on the plates also are witnesses to the plates as well as to Joseph's translating them.
Emma said of the time during the translation, “the plates often lay on the table without any attempt at concealment, wrapped in a small linen table cloth, which I had given him [Joseph Smith] to fold them in. I once felt of the plates, as they thus lay on the table, tracing their outline and shape. They seemed to be pliable like thick paper, and would rustle with a metallic sound when the edges were moved by the thumb, as one does sometimes thumb the edges of a book. … I did not attempt to handle the plates, other than [through the linen cloth]. … I was satisfied that it was the work of God, and therefore did not feel it to be necessary to do so” (“Last Testimony of Sister Emma,” Saints’ Herald, Oct. 1, 1879, 290; spelling standardized).
She also witnessed of the translation, “No man could have dictated the writing of the manuscripts unless he was inspired; for, when [I was] acting as his scribe, [Joseph] would dictate to me hour after hour; and when returning after meals, or after interruptions, he would at once begin where he had left off, without either seeing the manuscript or having any portion of it read to him.” (Emma Smith, interview by Joseph Smith III, Feb. 1879, Saints’ Herald (periodical published by the Reorganized Church of Jesus Christ of Latter Day Saints, now called Community of Christ), Oct. 1, 1879, p. 290.)
Oliver bore his witness, "To [sit] under the sound of a voice dictated by the inspiration of heaven, awakened the utmost gratitude of this bosom! Day after day I continued, uninterrupted, to write from his mouth, as he translated with the Urim and Thummim, or, as the Nephites would have said, 'Interpreters,' the history or record called 'The Book of Mormon.'” (Joseph Smith - History, footnote)
Martin Harris took a copy of the characters from the Book of Mormon to Charles Anthon and Samuel Mitchell, who also witnessed to him that the characters were "Egyptian, Chaldaic, Assyriac and Arabic" (although Professor Anthon retracted his witness after hearing of an angel's involvement). (Joseph Smith History 1:64-65)
Oliver and Martin, along with David Whitmer also had the privilege of being eye witnesses to the plates, even being shown them by an angel - which gives further evidence to Joseph having been given them by an angel in the first place. David Whitmer witnessed, “It was in the latter part of June, 1829. Joseph, Oliver Cowdery and myself were together, and the angel showed them [the plates] to us. … [We were] sitting on a log when we were overshadowed by a light more glorious than that of the sun. In the midst of this light, but a few feet from us, appeared a table upon which were many golden plates, also the sword of Laban and the directors. I saw them as plain as I see you now, and distinctly heard the voice of the Lord declaring that the records of the plates of the Book of Mormon were translated by the gift and power of God.” (Cook, David Whitmer Interviews, 63. Quoted here.) Martin Harris had a similar experience a short while later. These three witnesses gave their names to the world in the "Testimony of the Three Witnesses" published in the introductory pages of the Book of Mormon.
Eight other men received the opportunity of viewing the plates, not by an angel or with the voice of the Lord, but Joseph showed them and allowed them to turn the pages and handle them. Their witness to the world is also published in the introductory pages of the Book of Mormon.
Another witness to the plates was Mary Whitmer. "A grandson of Mary Musselman Whitmer (wife of Peter Whitmer Sr.) reported that Mary had 'so many extra persons to care for' that she 'was often overloaded with work.' One evening, after a long day’s work, she went to the barn to milk the cows and met a stranger who 'showed her a bundle of plates' and 'turned the leaves of the book of plates over, leaf after leaf,' promising Mary that 'she should be blessed' if she were 'patient and faithful in bearing her burden a little longer.'" (Andrew Jenson, “Still Another Witness,” in Andrew Jenson, ed., Historical Record: A Monthly Periodical, vol. 7, nos. 8–10 (Oct. 1888), 621. Quoted here)
Twelve people, besides Joseph, saw the plates, while others handled them or were witness to Joseph's actions in regard to them. Were the plates a hoax? Did Joseph somehow create the plates himself from metal? This is highly unlikely. Due to the poverty of himself, his friends and his family, and the many hardships and the scorn that he endured because of his claims, it is very unlikely that he would have persevered in those claims for so long had they been false.
The Book of Mormon itself is a witness that the plates existed and that the book was not written by Joseph Smith himself. How could a young farmer, with very little education have written the book as he did, recited to a scribe with no revisions or edits, all within the space of just a few months? Some who have studied the book have added their witness of the existence of similarities to Egyptian historical texts and the apocrypha. (See Hugh Nibley, Since Cumorah.) Others have pointed to archaeological "proofs" of its truthfulness that Joseph could not have known at the time. (see here for an example). I have even heard it said that each writer of the Book of Mormon had his own distinct writing style. (See here for an analysis) And, of course, there are millions of people who can give their witness to having received guidance, inspiration and hope from the words written in the Book of Mormon.
4. Other Witnesses of the Restoration. Joseph was no longer alone when he received the Aaronic Priesthood, was baptized, or when he received the Melchizedec Priesthood. In these things, Oliver Cowdrey served as a second witness to the events of the restoration. At the dedication of the Kirtland temple, many people witnessed angels, a bright cloud and a pillar of fire. Sidney Rigdon shared the vision of Christ and the kingdoms of glory recorded in D&C 76. One of my own ancestors, Edmund Ellsworth, was present when Brigham Young was revealed to be the next leader of the saints. He witnessed, "I was present at the meeting which heard President Sidney Rigdon. I plainly saw the mantle of Priesthood fall upon President Young with its power and spirit. The testimony of this was given to most of the congregation." (Biography of Edmund Lovell Ellsworth) Many others witnessed miracles, revelations, and prophecies made and fulfilled.
Just because these events took place and were witnessed two hundred years ago does not make their witness any less relevant today. How would we know anything that occurred so long ago except by the witnesses that have been passed down through time? These witnesses add to the witness of the Holy Spirit that these things are true.