One value of the Wolffian metaphysical triplet of soul, world, God is that it articulates three ways of necessary existence, or three ways in which something cannot not be. Whatever we attain to by the Cartesian cogito counts as soul, but whatever is common to your experience and my own is other than this. Again, just as it makes no sense to doubt the existence of soul as Descartes understands it (the source of thought while thought occurs) it makes no sense to doubt the other of the soul, even if we consider this other nothing but a relation to a term owing its existence to mind, as Idealists do (The debate between the Idealists and Realists is really whether the extramental has an absolute or relative existence, not whether it has existence simply; since if we identify existence as such with absolute existence we would make relations absolute non-entities. Berkeley, it seems to me, is pretty clear about this – he doesn’t deny the existence of the world or matter but denies that is existence is absolute and of-itself) This “other than soul” can exist either analytically or not, if not, it is world; if so, it is God.
The crucial point in all of this is that all these things are said in the order of existence where existence is taken as opposed to what something is. What Descartes calls “soul” cannot be known to be soul in such a way as to divide it from the other things we might call it. As soon as we try to articulate what is doing the thought we have fallen away from the original, absolutely certain vision of the cogito. Again, the vision we have of “world” does not allow us to answer the question whether its being is absolute or relative. One critique of all this would be to point out that these ideas of soul, world and God all seem pretty vacuous: what is the value of seeing a soul that we cannot tell apart from self, and cannot tell whether it is material or not? What is the value of seeing a world that might, for all we know, have only a relative existence and not an absolute one? For all the strength of the critique, it cannot reach its intended term of denying any value to the existential judgment. It simply goes too far to say that, say, the cogito argument gives us no knowledge of something in the properly existential order. Explaining away the existential because it provides no information about what exists is a piece of philosophical oversimplification and trickery – one might just as well turn the tables on the argument and point out that it is meaningless to speak about what something is if it cannot exist in some way, thereby making all what questions mere extensions of existential ones.
Still, if existential awareness does not allow us to answer what the existents are, then how does this existential awareness divide into three different things? If we have an awareness of soul that cannot divide it from self, how can it divide it from God, or God from world? The safest answer is that existential awareness is always given in a mediated way to us, namely as mediated through some grasp of what exists, that is, we have to use at least the word “something” to articulate an existential judgment: e.g. “the cogito argument tells us about the existence of something”. Like all knowledge, existential awareness is in the knower according to the mode of the existence of the knower, and our existence is not pure existence but an existence mediated by being a finite what. Note that all this requires is that we take “pure existence” as an idea which is useful in explaining why all of our existential judgments are mediated by essentialist ones, though there are all sorts of illuminating concepts which concern realities that do not or cannot exist.
Or is there even a simpler answer? No one could grasp existence without seeing some division between the necessary and contingent, the causal and the caused, the of itself and of another, etc. The cogito requires that “some existence be necessary”, but we can feel the slipperyness of the language when we say this – it’s not as if we wanted to say that the way in which the cogito reveals a necessary existence is the only way in which existence can be necessary, and in fact, we more want to divide the sort of existence revealed in the cogito from necessary existence. It’s not as if anyone wants to argue that “an existential awareness” is nothing but a mechanical voice saying “it is” over and over. Taken in this way, we might say that our single and unified existential awareness can articulate three different ways of developing the necessity of existence. The cogito develops it in one way, and the sense that this cogito reveals or relates to some other can be developed in different modes of necessity.