in his earlier works Descartes was inclined also to refer to various images in the brain as ideas.[13] And though he abandons this use in his later work, that's not so much a change of view as a clarification. Continuing definition (3) above, he writes:

… [I]t is not only the images depicted in the imagination which I call ‘ideas.’ Indeed, in so far as these images are in the corporeal imagination, that is, are depicted in some part of the brain, I do not call them ‘ideas’ at all; I call them ‘ideas’ only in so far as they give form to [informant] the mind itself, when it is directed towards that part of the brain. (2nd Replies, II.113, AT VII.160-1)

[I]n no case are the ideas of things presented to us by the senses just as we form them in our thinking. So much so that there is nothing in our ideas which is not innate to the mind or the faculty of thinking …. Nothing reaches our mind from external objects through the sense organs except certain corporeal motions … But neither the motions themselves nor the figures arising from them are conceived by us exactly as they occur in the sense organs … Hence it follows that the very ideas of the motions themselves and of the figures are innate in us. The ideas of pain, colours, sounds, and the like must be all the more innate … for there is no similarity between these ideas and the corporeal motions [which cause their production]. (Comments, I.304, AT VIIIB.358-9)

Consequently these ideas, along with that faculty [of thinking], are innate in us, i.e. they always exist within us potentially, for to exist in some faculty is not to exist actually, but merely potentially … (Comments I.305, AT VIIIA.360)

In so far as the ideas are <considered> simply <as> modes of thought, there is no recognizable inequality among them … But in so far as different ideas <are considered as images which> represent different things, it is clear that they differ widely. (3rd Med., II.27-28, AT VII.40; cf. Principles I.17, I.198-9, AT VIIIA.11)

When M. Arnauld says ‘if cold is merely an absence, there cannot be an idea of cold which represents it as a positive thing,’ it is clear that he is dealing solely with an idea taken in the formal sense. Since ideas are forms of a kind, and are not composed of any matter, when we think of them as representing something we are taking them not materially but formally. If, however, we were considering them not as representing this or that, but simply as operations of the intellect, then it could be said that we were taking them materially, but in that case they would have no reference to the truth or falsity of their objects. (4th Replies, II.162-3, AT VII.232)

[T]here is an ambiguity here in the word ‘idea.’ ‘Idea’ can be taken materially, as an operation of the intellect, in which case it cannot be said to be more perfect than me. Alternatively, it can be taken objectively, as the thing represented by that operation; and this thing, even if it is not regarded as existing outside the intellect, can still, in virtue of its essence, be more perfect than myself. (Preface to Med., II.7, AT VII.8)

....... I think therefore I am... or I am therefore I think??