A unique doctrine of the Church of Jesus Christ of Latter-Day Saints is that of a pre mortal existence. We believe that we existed as spirits prior to our mortal life on earth. The church teaches that God is our Heavenly Father, and that He is the father of our spirits. We believe that Christ is the first born of all the spirit children of Heavenly Father.
The belief in Jesus as the firstborn spirit child of God suggests a sequence where Christ was first, and others came after. This spirit birth event must therefore take place at a point in time. And after that point in time - for all eternity - we will be a spirit child of God. But what manner of beings were we prior to this spirit birth event?
Joseph Smith taught that matter could not be created nor made, and that this is also the case with intelligence. And if we are eternal beings, as Joseph taught, then we must have existed in some fashion prior to a spirit birth. Many members of the church would refer to this pre spirit birth form of existence as being 'intelligences'. This term was probably first forwarded in a meaningful way by BH Roberts, and an article written by him was published in the Improvement Era and can be found here.
As far as I know, there has been little to nothing revealed to the world regarding what intelligences are. And I feel this can safely be made the subject of speculation, as long as it is regarded as speculative. I certainly do not claim any special knowledge or personal revelation in this area. But I would like to present what I see as a few possibilities as to what intelligences are. If we can agree for the moment that intelligences are what we were prior to a spirit birth event then models would include:
Intelligences and Spirits are the same thing.
This line of thinking suggests that perhaps a spirit birth is not a literal thing, and that a spirit birth event is nothing more than some type of covenant relationship between an intelligence/spirit and God. Spirit birth is then more of an adoption type of relationship. In this model, our full spirit bodies are eternal, and were never created nor made.
Intelligences are to Spirits as Spirits are to Mortal Bodies.
This model suggests that a spirit birth event provided a spirit body in which an intelligence could dwell in much the same way as our mortal birth provided a mortal body in which our spirits dwell. The possibility that intelligences might have some matter and form associated with them is maintained. As is the possibility of a literal spirit birth.
Intelligences as Spirit Matter.
This model would suggest that the matter that ultimately goes into the creation (or organization of) our spirit bodies is eternal. But that this spirit matter did not have an individual mind or will of it's own prior to spirit birth.
Intelligences as Free Will Itself.
This model would suggest that intelligences had no matter associated with them, yet exist eternally. A spirit birth event then provided this 'mind' or 'will' with a material form for the first time.
Well, those are the major possibilities as I see them. From what little I have read, it does not appear Roberts took much of a stand as to what intelligences are. McConkie seemed to be in the Intelligences as Spirit Matter camp. I currently favor the Intelligences are to Spirits as Spirits are to Mortal Bodies thoughts.
What think ye? Have I missed categories, or badly messed up the ones I presented?