Certain assumptions shared by Descartes' arguments for the existence of God, be the arguments a posteriori or a priori, are that the ideas of the infinite and the perfect are ontologically prior to the ideas of the finite and the imperfect, and that the ideas of the infinite and the perfect are innate to the human mind because they are implanted there by God. For example, for Descartes my idea that I think contingently (which is my idea of a finite and imperfect activity) presupposes an ontologically prior, innate idea of what it means to think necessarily (which is my innate idea of an infinite and perfect activity). Or, to understand that I think contingently (a finite and imperfect activity) requires that I must have some ontologically prior, innate understanding of what it means to think necessarily (an infinite and perfect activity). However as this line of reasoning relates to my central theme, I would submit, contrary to Descartes' position, that my understanding of the idea of necessary thinking activity (an infinite and perfect activity) is NOT innate to the human mind and is NOT implanted there by God.
Neither is the idea of my contingent thinking activity (a finite and imperfect activity) obtained, as Descartes would claim, by limiting or bounding, in some way, the ontologically prior, innate idea of necessary thinking activity (an infinite and perfect activity). Instead, my idea of necessary thinking activity is a direct result of my deliberate attempt to try to remove, albeit unsuccessfully, that characteristic from the idea of my contingent thinking activity which limits and constrains it; viz., its vulnerability to the possibility of complete cessation and non-existence. This, I submit, is the genuine way in which I arrive at an understanding of the idea of necessary thinking activity (an infinite and perfect activity).
Nevertheless, it does not necessarily follow, either from the former interpretation of Descartes or from my latter interpretation, that I can have a DIRECT PERSONAL EXPERIENCE of necessary thinking activity (an infinite and perfect activity) in the same way as I do, in fact, have a DIRECT PERSONAL EXPERIENCE of contingent thinking activity (a finite and imperfect activity).
As I see it, the central issue is not a matter of the possibility of my being able to have, or not to have, an IDEA of perfect thinking activity or an IDEA of perfect being - be those ideas innate, adventitious, or factitious. Instead, the central issue is a matter of the possibility of my being able to have, or not to have, a DIRECT PERSONAL EXPERIENCE of that perfect thinking activity or of that perfect being.
Or, approaching it from a slightly different direction, doubts and desires may come from an understanding that I lack something, and that I would not be aware of that lack unless I was aware of a more perfect being that has those things which I lack. However, my ability to have an IDEA of, or CONCEPTION of, or UNDERSTANDING of, or AWARENESS of a more perfect, or infinite, being that possesses all those things which I lack (inclusive of necessary thinking activity), does not mean that I am also able to have a DIRECT PERSONAL EXPERIENCE of that being and its necessary thinking activity in precisely the same way as I am able to have a DIRECT PERSONAL EXPERIENCE of my being and its contingent thinking activity.
Certainly, I can postulate the existence of a being that thinks necessarily and exists necessarily, but I cannot have a DIRECT PERSONAL EXPERIENCE of the necessary thinking activity which would simultaneously yield an intuition of the indubitably certain existence of such a necessary being. Again, I CAN PERFORM the "Cogito contingenter, Sum contingenter," but I CANNOT PERFORM the "Cogito necessario, Sum necessario."
In conclusion, I submit that Descartes' a priori argument for the existence of God is not an experientially grounded performative argument like the one he formulated to successfully and persuasively prove the existence of the human being. His ontological argument, lacking the crucial, indispensable, experiential foundation of necessary thinking activity, is destined to fail from its very inception. It is a non-persuasive, quasi-intuitive argument espousing a so-called self-validating idea of God which is given in consciousness and which represents God as existing, but which, in fact, completely misses the mark.