I’ll never forget the day when, as a new member baptized maybe three months ago, missionaries showed up at my apartment to ask me what the different was between the godhead as spelled out by the Articles of Faith and the trinity as believed by orthodox Christianity. Part of the reason it’s an episode burned into my mind is that I was so shocked that these poor missionaries who had gone through the Missionary Training Center, one who was on the tail end of his mission, did not understand basic Mormon theology. For all you orthodox Christians out there who read this, let this be a lesson for you when you speak to Mormons before you accuse them of lying or being brainwashed. The reality of the situation is that many Mormons, maybe the majority, do not understand basic Mormon theology anymore. For you Mormons, you may argue that the doctrine of the trinity just doesn’t make sense, it’s a contradiction in terms, and that’s why there is confusion.
Let’s start with the trinity. The grounding assumption of any formulation of the trinity starts with the assumption that there is but One God. By God here I mean the immutable, infinite, eternal, necessary being labeled God. There are two ways to come to this conclusion, through philosophy and through exegesis of the Bible. Through philosophy you can come to suspect that the God I stated above exists through classic arguments such as the argument from contingency or the ontological argument. It follows from such arguments that there would be only one such being, as a truly infinite, necessary, immutable being would be a true unity. From the Bible verses from especially deutero Isaiah and the New Testament, when monotheism was firmly established in Israel, reaffirm the notion that there is but one God.
With that established, the next thing integrated into the notion of the trinity is usually the Son, Christ. Again, there are two ways of approaching this problem, through philosophy and exegesis of the Bible. Through philosophy you may come to some notion of a finite creation separated from its infinite Creator and the question as to how to close that gap between two qualitatively different types of beings. The incarnation is one particularly appealing solution, and since it is testified to in the New Testament, appears to many Christians to be particularly powerful. From statements in the New Testament, most powerfully from John 1, it is understood that Christ is the expressed Logos, or spoken Word/reason/mind of God somehow enfleshed. It follows from the notion that there is but One God, that there must be some kind of profound unity between the creator God and this enfleshed Logos. There are a couple ways to do this, the easiest way mentally is through modalism/oneness theology, which states that God expresses himself through different modes of being- the father first, the son second and the holy ghost third. Hence, Jesus IS the father IS the holy ghost. That melding of persons into one person doesn’t prove satisfactory to all however, since through exegesis most Christians argue that Christ was a bonafide separate person from the Father (i.e. who was Jesus praying to when praying to the Father? It seems reasonable to assert it was a different person).
This is where it getes tricky and the doctrine of the trinity loses many well meaning people. How can you possibly assert that two separate persons are the same Being? Because recall, it was already established that there is only One God. The notion of personhood is a tricky enough one to begin with. What does it mean that youare a person when you are not made up of the same ‘stuff’ one year to the next as your cells are created and destroyed? Is there a difference between a person and a being? Usually when we talk about personhood we mean a rational agent, and when we talk about being we describe qualities. To be a human being is to be a person with a mortal, finite body. To be a human being is to be a a person and a particular being in unity. But, what if there was a type of being which was unlimited, infinite, is it possible that multiple persons could share the exact same nature? Think about this for a second, part of being a human being is being finite and imperfect- separate, distinct. But if a rational agent has an infinite, immutable being, what’s to say that another rational agent, another person, could not share that exact same being of infinity? There can only be one such being- multiple, perfect infinites would actually overlap and become the exact same beings, they would overlay each other or become contradictions in terms- but why not have multiple persons be that being? From there comes the inclusion of the Holy Spirit as a third person to be the being of God. From what I can tell, the inclusion of the Holy Spirit is primarily due to exegesis from scripture.
Whether or not you agree with the above, I hope you realize that it isn’t just silly, impossible nonsense. It’s reasonable enough. Now how does that compare to the Mormon notion of the Godhead? Simple. The Mormon Godhead supposes that there are three beings which compose it, not just three persons in one being. This is made possible because deity in Mormonism is not infinite in the absolute sense. It is infinite only in a relative sense- in the same way that a large sheet might as well be infinite to a speck of dust. Therefore it is not contradiction in terms to assume that there can be multiple relatively infinite beings, it is only a problem if you suppose that there is an absolutely infinite being in existence.