What is Nietzsche's source of immediate knowledge in Beyond Good and Evil?

Question

In Beyond Good and Evil, Section 16, Nietzsche uses "immediate certainties" in quotation marks. Who and from where is Nietzsche quoting this, or is he using the quotations marks to speak ironically? My suspicion is Kant. It would be helpful if could provide as accurate a source as possible.

The section begins as follows and here is a link to the entire section if needed.

There are still harmless observers of themselves who believe that there are "immediate certainties," for example, "I think," or that superstition of Schopenhauer's, "I will," just as if perception here was able to seize upon its object pure and naked, as "thing in itself," and as if there was no falsification either on the part of the subject or on the part of the object.

Answer 1

Nietzsche's source for "immediate certainty" is probably Descartes. It was through Descartes that the link between the immediacy of "observing oneself" and certainty became an important theme and an ongoing topic of debate for subsequent modern philosophy. Here is a more precise excerpt from Descartes's Principles of Philosophy.

IX. What thought (cogitatio) is. 
By the word thought, I understand all that which so takes place in us that we of ourselves are immediately conscious of it; and, accordingly, not only to understand (intelligere, entendre), to will (velle), to imagine (imaginari), but even to perceive (sentire, sentir), are here the same as to think (cogitare, penser). For if I say, I see, or, I walk, therefore I am; and if I understand by vision or walking the act of my eyes or of my limbs, which is the work of the body, the conclusion is not absolutely certain, because, as is often the case in dreams, I may think that I see or walk, although I do not open my eyes or move from my place, and even, perhaps, although I have no body: but, if I mean the sensation itself, or consciousness of seeing or walking, the knowledge is manifestly certain, because it is then referred to the mind, which alone perceives or is conscious that it sees or walks. 

In addition, Nietzsche's first example "I think" probably refers to Descartes's related Cogito argument: "I think, therefore I am".

Answer 2

I have erased some of my over-the-top comments and I am writing a short answer really to put Barinder's question back on top again because it was a good question.

My feeling is that Nietzsche is writing an anti-philosophy, and that he would suggest that we humans operate on the level of the instincts. The only check on this would be the true ascetic aristocratic mode of being. The true aristocrat was after land and he was a warrior, not a thinker. Rarely will you find an aristocrat and a thinker in one person, though Descartes had the misfortune of running across one with a very cold library.

Aristocrats fight for what they want, and they satisfy their instinctual urges without any qualms, but this requires a warrior spirit and this requires a fit body, and this may require a somewhat asetic life. We philosophers (who know our Nietzsche) are called to give up our thinking, and our word play to to become this kind of "philosopher-aristocrat", if you will. This is very much Nietzsche's version of the philosopher king, not Plato's.

The second point would be on Descartes' "I", and whether perhaps Nietzsche had studied some Buddhism (idea from Schopenhauer?), and that Nietzsche began to question the idea of the "I" in Descartes (i.e. Buddha would say no "I", no ego, it is not to be found). At any rate, if Buddhism worked to calm Schopenhauer's Will, it would actually defeat Nietzsche's larger project of turning man into an instinctual doer, with the only possible check against the gross display of instinct being the temperament of the true aristocrat (the ascetic, warrior temperament, not a life of luxury and gluttony).

Of course, Nietzsche could not actually "insist" on anything it seems to me, at bottom, his philosophy or anti-philosophy says all facts are interpretations, and this is itself an interpretation...so this is doing, instincts and not thinking, with all the problems and benefits that come along with doing and not thinking.