In the April 2008 General Conference Mormon apostle Jeffrey R Holland said:
“The fact of the matter is that virtually every prophet of the Old and New Testament has added scripture to that received by his predecessors…If one revelation to one prophet in one moment of time is sufficient for all time, what justifies these many others? What justifies them was made clear by Jehovah Himself when He said to Moses, ‘My works are without end, and . . . my words . . . never cease.’
“I testify that Thomas S. Monson is God’s prophet, a modern apostle with the keys of the kingdom in his hands, a man upon whom I personally have seen the mantle fall. I testify that the presence of such authorized, prophetic voices and ongoing canonized revelations have been at the heart of the Christian message whenever the authorized ministry of Christ has been on the earth.”

Mormons believe that they work from an open canon to which revelation is added.
“There are those who would assume that with the printing and binding of these sacred records that would be the ‘end of the prophets’. But again we testify to you that revelation continues and that the vaults and files of the Church contain these revelations, which come month to month and day to day. We testify also that there is, since 1830 when the Church of Jesus Christ of Latter-day Saints was organised, and will continue to be, so long as time shall last, a prophet, recognised of God and His people, who will continue to interpret the mind and will of the Lord” (“Revelation: The Word of the Lord to His Prophets,” Spencer W Kimball, Ensign, May 1977, 78).

However, there has been no written prophecy since:
1918 – Joseph F Smith’s vision of Jesus’ visit to the dead while his body lay in the tomb; D&C 138
1847 – Brigham Young’s revelation at Winter Quarters regarding the organisation of the saints; D&C 136
1844 – An account (not a revelation) of the “martyrdom” of Joseph and Hyrum Smith; D&C 135
1843 – Four revelations regarding (1) how to distinguish angels (D&C 129);( 2) eternal marriage (D&C 132); (3) Three degrees of glory (D&C 131); (4) The Second Coming, the celestial earth and the law of eternal progression (D&C 130)
It seems that 1918 saw the last doctrine-defining revelation in the Mormon Church, a gap of 90 years, and before that, 1847 saw the last church-directing revelation, a gap of 153 years. Inevitably a Mormon will mention the 1978 revelation on Priesthood, but the Doctrine and Covenants contains no “canonised” revelation, just a “Declaration”. This is also true of the 1890 decision on polygamy, reversing a so-called eternal principle; a Declaration but no “canonised” revelation. Is it right to be satisfied that it is “in the vaults and files of the church” and not broadcast to the church and the world? If Christianity has proved apostate in not adding to the canon of Scripture, and Mormonism is the restoration of revelation, why has there been nothing of significance added to the Mormon canon for 90 and 153 years?
The result has been a major change in tone.
Where once Mormon prophets declared:

“We talk about Christianity, but it is a perfect pack of nonsense. … It is a sounding brass and a tinkling cymbal; it is as corrupt as hell; and the Devil could not invent a better engine to spread his work than the Christianity of the nineteenth century.” (John Taylor, Journal of Discourses, vol. 6, p. 167, 1858)
Now they say to Christians:
“Bring the good that you have and see if we can add to it” (Gordon B Hinckley, TV Interview, Larry King Live)
Where once Mormon prophets declared:
“Verily, thus saith the Lord…”
Now they say:
“Let me tell you a story; Brother Joseph once said…”
Mormonism has moved from the abrasive to the avuncular, from the emphatic to the empathetic, from exclusive to inclusive, from the prophetic to the pedagogic.
Amateur apologists, not prophets, are making Mormon doctrine:
Mormon “Para-church” organisations like FAIR are making the running in defending Mormonism against critics. While the Mormon leadership does occasionally publish statements to clarify issues raised in the press etc., they never meaningfully engage with these issues. FAIR, on the other hand, is consistently engaged in producing apologetics and rebuttals in response to church critics. When a Mormon defends his position it is FAIR and similar “unofficial” sources that will have shaped his thinking not the prophet.
FAIR (Foundation for Apologetics, Information and Research) aims “to address the charges levelled at the doctrines, practices and leaders of The Church of Jesus Christ of Latter-day Saints (Mormons) with documented responses that are written in an easily understandable style. FAIR will use current scholarship, scripture, Church doctrine, historical literature and sound logic in constructing faithful, well-reasoned answers.” Ironically, the text they use on their Internet home page is Ephesians 4:11-14, a key, yet increasingly incongruous, proof text for Mormon claims to continuing revelation.
FAIR emphasise scholarship and research and enjoys a considerable reputation among Mormons, but lays no claim to revelation, and issues the usual disclaimer:

 “FAIR is not owned, controlled by or affiliated with The Church of Jesus Christ of Latter-day Saints. All research and opinions provided on this site are the sole responsibility of FAIR, and should not be interpreted as official statements of LDS doctrine, belief or practice.”
Past Doctrines have become cultural aberrations:
Brigham Young famously taught that Adam was God (Brigham Young, Journal of Discourses, volume 1, p. 50)
FAIR has (unofficially) said
“Brigham claimed to have received these beliefs by revelation, and, on at least three occasions, claimed that he learned it from Joseph Smith. While this doctrine was never canonized, Brigham expected other contemporary Church leaders to accept it, or at least not preach against it. (Orson Pratt did not believe it, and he and Brigham had a number of heated conversations on the subject.)
“The historical record indicates that some contemporary Latter-day Saints took Brigham’s teachings at face value and attempted to incorporate the doctrine into mainstream LDS teachings. This response was far from universal, however, and lost steam after the turn of the 20th century.” (FAIRWIKI on Adam/God)

NB It is telling that FAIR goes on to offer a variety of possible “explanations” for the Adam/God doctrine that have developed over the last century but the Mormon Church can offer no official exposition on the subject.
The Mormon canon states:
“. . . he that abideth not this law (polygamy) can in no wise enter into my glory, but shall be damned, saith the Lord.” (D & C, 132:27)
Brigham Young taught:
“The only men who become Gods . . . are those who enter into polygamy.” (Brigham Young, Journal of Discourses, vol. 11, p. 269)
But FAIR has (unofficially) said:
“To obey the Lord’s commands in all things is necessary for exaltation. Members of the Church in, say, 1860 who refu
sed to follow the counsel of prophets and apostles, put their spiritual standing in jeopardy. Likewise, members who refuse to obey present counsel are at risk. This does not mean that present members of the Church believe that the principle of plural marriage is false—rather, they believe that it is a principle only to be practiced when the Lord commands it for His purposes.” (FAIRWIKI article on polygamy)

Racist Doctrines
Joseph Fielding Smith taught:
“There is a reason why one man is born black and with other disadvantages, while another is born white with great advantages.  The reason is that we once had an estate before we came here, and were obedient, more or less, to the laws that were given us there.  Those who were faithful in all things there received greater blessings here, and those who were not faithful received less.” (Joseph Fielding Smith, Doctrines of Salvation, vol.1, p.61)
But FAIR now (unofficially) teaches: From our perspective as “enlightened” people of the early twenty-first century, virtually everyone in America up until the last few decades — prophets and other LDS leaders included — held beliefs that we could now consider racist. But that was the culture of the times, and we, like the rest of society, have progressed to become better people in this respect, more tolerant, more accepting. Fifty years from now, people will probably look back at our time and say, “How could they have been so bigoted?” Or, “How could they have missed issue X, which seems so clear to us now, in retrospect?” (FAIRWIKI article on Negroes and the priesthood)

If continuing revelation is the hallmark of “the true church”, what does its absence say? If the Mormon Church is led by prophets, why is all the doctrinal development being done by Para-church organisations?
The typical Mormon Apologetic
This leaves the Mormon with the conviction of continuing revelation but the reality of a closed canon of Scripture in his hand; and he doesn’t know how to sit under the authority of Scripture. To him, it is always second hand, revelation for yesterday, because he is “led by a prophet.” Consequently, the typical Mormon apologetic is almost entirely refutation, rather than exposition, because he doesn’t have modern revelation to expound, but increasingly implausible claims to defend.
Exposition: To expound is to lay open the meaning of; to confirm and prove. In the context of teaching and preaching this means expounding or explaining the truth of scripture.
Refutation is the act of refuting or denying something.
There are four steps to the Mormon apologetic:
Critics say…
But they are anti-Mormon (it can’t be true because they said it)
We truly know/don’t really know (assertion not exposition)
Here is the truth/a straw to clutch (have faith)
Where a Christian would begin with the truth, a Mormon starts with the critic; where a Christian would continue with an appeal to biblical authority, the Mormon would go on to discrediting the critic; where the Christian would present “many proofs” (Acts 1:3), the Mormon offers a series of uncorroborated assertions; where the Christian expects faith to be based on reasoning from Scripture, the Mormon ends with an appeal to blind faith based on feelings.
Since sound exposition is not in the Mormon’s tool box, then a demonstration of sound exposition is important.
It makes their refutations look poor by comparison and the stark contrast will give them pause for thought.
It demonstrates the strength of Scriptural proofs, many of which will be unfamiliar to the Mormon, and models what it is to put a high value on Scripture.
Mormons will cite isolated Bible verses to “prove” their point but a careful reading around their proof texts will give context and true meaning within the wider context of God’s word and lead to a clear understanding of the truth. A confidence in, and competence with, the Bible is essential in witnessing to Mormons and it is important to recognise that almost every issue you will tackle in conversation with a Mormon will have been addressed in its pages, as well as in the councils and deliberations of the early Church. More reason, if any were needed, for knowing your Bible and knowing something about the history of the Christian Church.