To paraphrase Nietzsche: Sum, ergo cogito, bitch.
From a Nietzschean perspective, Descartes’s Meditations on First Philosophy is riddled with flaws, based mainly in his many presuppositions and failure to enact doubt totally. Specifically, Descartes' main line of argument, which can be summarized in his claim "Cogito Ergo Sum", is only possible because of his a priori concept of thinking (cogito) which is already derived from a concept of existence (sum) — both of which are mere social constructions. Furthermore, both concepts are only valid within the specific realm of language and reason Descartes presupposes; therefore, Descartes does not apply doubt to the conceptualization of existence, thinking, consciousness, etc. Moreover, Descartes' cogito is not at fault solely for its necessitation of metaphysical foundations; his dissociation of the 'I' from 'think' and, thus, from the Will to Power is also dubious as "a thought comes when ‘it’ wants, not when ‘I’ want; so that it is a falsification of the facts to say: the subject ‘I’ is the condition of the predicate ‘think’” (BEYOND GOOD AND EVIL 47 ish).
Beginning in his First Meditation, Descartes writes that, "it was necessary, once in the course of my life, to demolish everything completely and start again right from the foundations if I wanted to establish anything at all in the sciences that was stable and likely to last" (CITE). As such, he asserts that his method demands the removal of preconceived opinions/notions. Descartes, later, states, “knowledge is to be based in complete, or perfect, certainty amounts to requiring a complete absence of doubt—an indubitability” (MFP 3). Essentially, by applying this methodology of doubt, Descartes' Meditations sought to reach some sort of scientific certainty through a rejection of any opinions that may arise doubt, or questioning, of some sort. Descartes’ Meditations contain many specific necessitations/claims including: a self-determined subject; the search for truth; full awareness during the meditation process in order to arrive at the cogito; and reason as innate. These claims in particular are the crux of the following critique.
Perhaps the most striking point against Descartes' meditations comes from the conflict between his self-proclaimed doubt and the presupposition of the 'I' as being self-determined. This is evidenced from the first line of the first Meditation, when Descartes writes, "Some years ago I was struck by the large number of falsehoods that I had accepted as true in my childhood, and by the highly doubtful nature of the whole edifice that I had subsequently based on them" and continues throughout (CITE). Descartes conceives of an 'I' as the cause of thought — an 'I' that is not the result of the Will to Power, but, rather, a priori to it. The Nietzschean 'I', on the other hand, is the manifestation of various drives — which are 'given' by the Will to Power in a body in the state of constant becoming. Singularity comes only from the particular constitution of those drives, although they are the result of constantly changing conflict among multiple forces. Hence, Descartes' language directly opposes the social ontology that, essentially, denies metaphysics except on the point of the Will to Power; there are no transcendent features of humanity that are true in all times and places (as human ontology is a social construction), but instead human beings are driven by a desire to master — especially to reinterpret or be creative. Thus, Will to Power — the conflicts among multiple forces in the process of constant change — is entirely deterministic. In fact, one cannot, as Nietzsche notes, know what is going on "under skin" (i.e. Will to Power qua Will to Power), but may only interpret and observe the "skin" itself (i.e. individual manifestations of Will to Power). Considering, Descartes does attempt to remove himself from the entities of social constructions (language, values, pre-established concepts, etc.), but does so in an attempt to reflect only the externals of what is happening “under skin” (Will to Power), where these usual human concepts have no validity. As such, Descartes' methodology falls short of fully doubting due to its reliance upon the 'I' as a distinct, a priori device.
In deeming 'to think' an outcome of one’s drives, Nietzsche does not accept an 'I' who is self-determined (a conscious Ego who commands mental states), but, instead, an 'It' that thinks. Accordingly, the 'I' is a useful narrative that is secondary to the “It”, which is the manifestation of Will to Power; such an 'I' is simply one’s interpretation of one’s drives which we, incorrectly, isolate from the whole. If certainty is sought, being aware that one is thinking requires a relationship with other subjects and objects; so, if Descartes’ thinking thing is possible, is it the case that if one were alone in this world one would be aware that one is thinking? This seems a questionable claim. Consider, perhaps, a girl who, when she was, say, 5 years old, was convinced that she got a bead stuck in her ear. She distinctly remembers it being put in. But, as she tells other people, they are convinced she is lying. Over the years, they continue to tell her she made the story up. And when she goes to the doctor for check ups, they never mention anything. So she begins to question if it ever really happened, until one day she feels pressure in her head years later and, all of a sudden, when she goes to get her ears cleaned a bead pops out. Although the girl was aware that she had a bead in her ear, she was led to self-doubt because those around her tried to convince her otherwise. So, while the girl did not necessarily doubt her very existence, her certainty, perhaps even her 'consciousness', was thrown into question because she lacked outside reference points. It returned only in seeing the bead come out of her ear again — an external object on which the girl could rely. This story suggests a possibility that is the very opposite of Descartes’ approach: that there appears to be no such entity as 'I' without an external reference. Descartes conceives of the subject as self-determined, as a cause, and thus succumbs to Nietzsche’s critique. Hence, Nietzsche’s “Sum, ergo cogito” proposes that the condition in which it is possible to have what is called an 'I' is only if there is a 'we' or an external world.
One then, as Nietzsche does, begins to take issue with conceiving of a thinking thing as having a faculty that can cause and command mental states; because what delimits the whole being as a fictional Ego is social construction (words, concepts, structured content), but this fictional Ego remains only a 'visible' conceptual expression of the whole. It is not the case that because one cannot conceptualize some unconscious states, one cannot conclude that these states do not exist or are subordinate to conscious states, nor is it the case that the conscious states constitute an Ego apart from and commanding the unconscious states. Descartes’ cogito represents just one aspect of the self that can be grasped only with an already given concept. Hence, Nietzsche’s “Sum, ergo cogito” conveys the whole mental status (unconscious and conscious states) highlighting that it is an a priori conceptualization, which condition makes possible Descartes’ “Cogito, ergo sum” as a superficiality.
In all, Descartes’ cogito is but a partial picture of one’s mental status and has a certain validity only as a reflection of the human surface and a product of language (superficiality of consciousness); otherwise, it does not work without Descartes’ pre-established metaphysical values. In fact, from Nietzsche’s standpoint, it is quite unconvincing to start from the Cartesian principle that the 'I', existing as an entity, is a cause of thinking, since this seems to rest on preconceived assumptions regarding both a self-defined subject and that subject’s operations. More generally, Nietzsche observes that Descartes’ Meditations is replete with metaphysics, something Nietzsche vehemently criticizes. Descartes’ 'I' is merely a fictional Ego which expresses only conscious states (words, concepts, structured content) and does not take into account the unconscious ones. Moreover, in order to arrive at existence Descartes effectively departs from social constructions (conscious states, language, and concepts) without subjecting these concepts to doubt. In that sense, Descartes does not go beyond the surface, which provides reason for the negative side of Nietzsche’s appraisal of him as superficial. In re-ordering Descartes, Nietzsche contends for a being a priori (something going on under skin, unconscious states) before considering the surface (conscious states, conceptualization, social construction). Nietzsche, therefore, is correct in stating that Descartes’ “Cogito, ergo sum” is only possible as a suffix. As Nietzsche re-states it, “Sum, ergo cogito: cogito, ergo sum” (Gay Science 223).