The question here is whether the word then should go at the end of the preceding if- clause or at the beginning of the following interrogative clause. The 1830 edition attached the then to the following wh- question that begins with why; the RLDS text has continued this punctuation. In this case, the then means ‘as a consequence’. The 1852 LDS edition, on the other hand, changed the punctuation by placing the comma after the then, which the LDS text has maintained. With this change, the then now means ‘in the past’, and the reference is to the last clause in the preceding verse:
In other words, verse 19 basically asks: “If there were miracles wrought then [at the time of the apostles], why has God [now] ceased to be a God of miracles?” As pointed out by Don Brugger (personal communication), the 1852 interpretation here in Mormon 9:18 is possible since there is a semantically equivalent example where the adverb of time is represented by the phrase “at that time”:
Yet the adverb then, meaning ‘in the past time’, was not chosen in Alma 12:23.
Although either reading will work in Mormon 9:19, internal evidence argues that the earlier 1830 punctuation is correct. First of all, there are eight examples elsewhere in the text of then why occurring as a unit at the beginning of a clause. And in two cases, there is a preceding if- clause:
In the last case, the comma could have been placed after the then, just as it was in the 1852 LDS edition for Mormon 9:19. Yet in Helaman 8:12, the 1852 editors consciously decided (in the second printing) to place a comma before the then. For the subsequent LDS edition (in 1879), that comma was omitted, perhaps intentionally, as if to allow for then to end the preceding if- clause. But the 1920 LDS edition restored the comma to the LDS text, placing it before the then.
For the remaining six cases of then why, there is no doubt that the then belongs with the following why- clause, especially in three cases where there is an exclamatory O (just like in Jacob 4:9, listed above):
More importantly, except for the two theoretical cases in Helaman 8:12 and Mormon 9:19, the adverb then never ends a clause anywhere else in the Book of Mormon text (in other words, in the only places where it theoretically could end a clause, then is immediately followed by why). In two cases, we get then after the subject but before the verb phrase; both of these occur in biblical quotes:
In a third case, the then comes after the direct object, but before a long adverbial phrase that ends the clause:
And finally, there is one instance of the phrase “now and then”; in that case, this adverbial phrase comes right after an existential “there was”:
But in 218 other cases, the then comes at the beginning of the clause (in 113 of those cases there is a sentential connective or conjunction, such as and, O, yea, and behold ). The placement in the 1852 LDS edition of the then at the end of the if- clause in Mormon 9:19 is therefore unique for the Book of Mormon text. And even that edition did not change the punctuation in Helaman 8:12, when in theory it could have. Here in Mormon 9:19, the critical text will adopt the normal placement of the then, so that we end up with a ninth instance of then why in the text. Similarly, the punctuation for Helaman 8:12 will be maintained.
Summary: Change the punctuation in Mormon 9:19 so that the then comes at the beginning of the following interrogative clause (“then why has God ceased to be a God of miracles”); this decision conforms to all other cases in the text where then occurs at clausal boundaries, including Helaman 8:12.