What were DesCartes's conceptions of objectivity & subjectivity?

Question

This summary of "Descartes's Basic Epistemological Argument" indicates his usage of the terms is different than a contemporary notion of objective as regardless of an observer and subjective as relative to an observer.

15. Therefore, for each thinker, that of which that thinker is certain is his or her own existence as a thinking thing. [Note the important move here: each potential knower, starts from a basic foundation alleged to be known only to him or her. This is the "subjective" turn of the "modern" period in contrast to objective or "metaphysical" starting point of the Ancient philosophers.]

...

17. Insofar as the existence of the thinking thing is indubitable, so equally indubitable is the existence of the ideas -solely as ideas- which the thinking thing is thinking. [Unfortunately the conception of the "existence" of a thing as an idea in some mind or another came to be called by the misleading label "objective reality" because it was a way of saying the thing exists as an object of thought; this leads to the strange way of speaking that if I think of something, that which I think of has 'objective reality.']

According to this article on his theory of ideas, it seems there is no "objective" in the contemporary or empirically verifiable sense of the term, and DesCartes objects are presentations made to the individual mind - like subjective "sense data" for lack of a better term:

The objective reality of a thing, on the other hand, is the reality a thing possesses in virtue of its being a representation of something

According to this article on his epistemology, the sense of "subjective" seems similar to the modern usage of objective and akin to a conflation of perspectivalism with knowledge:

If we take Descartes to be using ‘I’ to signify this subjective character ... the “I”-ness of consciousness turns out to be ... a primary datum of experience.

How did DesCartes conceive of and use the terms "objective" and "subjective"? Is his "cogito ergo sum" a representation of the subject as object?

Answer 1

Descartes did not use the word "subjective". He did use the word "objective", more or less as we would today use "subjective". He attributed to ideas (that is to sense data and concepts, the supposed inner entities of the mind) a distinct species of existence: objective existence. He contrasted this mode of existence with formal existence, which designates the existence of things in themselves, apart from minds. 

For just as this mode of objective existence pertains to ideas by their proper nature, so does the mode of formal existence pertain to the causes of those ideas. (Third Meditation)

Given this distinction, Descartes formulated the principle, that the level of perfection of an idea must be derived from the perfection of its external cause.

And although it may be the case that one idea gives birth to another idea, that cannot continue to be so indefinitely; for in the end we must reach an idea whose cause shall be so to speak an archetype, in which the whole reality [or perfection] which is so to speak objectively [or by representation] in these ideas is contained formally [and really]. (ibid.)

Descartes believed this principle to be self evident, and he used it in his proofs for the existence of God.

Apart from the special declension "objective", Descartes used the term "object" quite as we do, for an entity, a goal, or for anything that we perceive or think about.

At the same time I have before received and admitted many things to be very certain and manifest, which yet I afterwards recognised as being dubious. What then were these things? They were the earth, sky, stars and all other objects which I apprehended by means of the senses. (ibid.)

Similarly, Descartes used the term "subject" quite as we do, for a topic. But he did not use the term "subject" to designate the "I", just as he did not use the term "subjective" for "private, personal" as we do.