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René Descartes (1596–1650) was a French philosopher and mathematician, credited as a foundational thinker in the development of Western notions of reason and science. His philosophy was built on the idea of radical doubt, in which nothing that is perceived or sensed is necessarily true. The only thing that remains true that there is a mind or consciousness doing the doubting and believing its perceptions, hence the famous formulation, ‘I think therefore I am’, or in Latin, the cogito—‘Cogito ergo sum’. Descartes also proposed that the mind and body were two separate and distinct entities, but even the body was not so certain a thing as the mind, because, like everything else in the world, the body could only be sensed because there was a mind to sense it. In 1663, Descartes’ writings were placed on a list of prohibited books by the Pope, because of the central place Descartes gave to reason and mind, rather than God, in his philosophy. Here is his explanation of the centrality of the reasoning mind in knowledge making:

As I then desired to give my attention solely to the search after truth, I thought … I ought to reject as absolutely false all opinions in regard to which I could suppose the least ground for doubt, in order to ascertain whether after that there remained [anything at all] in my belief that was wholly indubitable. Accordingly, seeing that our senses sometimes deceive us, I was willing to suppose that there existed nothing really such as they presented to us …

[T]he very same thoughts (presentations) which we experience when awake may also be experienced when we are asleep, while there is at that time not one of them true, I supposed that all the objects (presentations) that had ever entered into my mind when awake, had in them no more truth than the illusions of my dreams. But immediately upon this I observed that, whilst I thus wished to think that all was false, it was absolutely necessary that I, who thus thought, should be somewhat; and as I observed that this truth, I think, therefore I am (cogito ergo sum), was so certain and of such evidence that no ground of doubt, however extravagant, could be alleged by the sceptics capable of shaking it, I concluded that I might, without scruple, accept it as the first principle of the philosophy of which I was in search … I thence concluded that I was a substance whose whole essence or nature consists only in thinking, and which, that it may exist, has need of no place, nor is dependent on any material thing; so that ‘I’, that is to say, the mind by which I am what I am, is wholly distinct from the body, and is even more easily known than the latter …

I considered myself as having a face, hands, arms, and all that system of members composed on bones and flesh as seen in a corpse which I designated by the name of body … By the body I understand all that which can be defined by a certain figure: something which can be confined in a certain place, and which can fill a given space in such a way that every other body will be excluded from it; which can be perceived either by touch, or by sight, or by hearing, or by taste, or by smell … [However,] I have thought I perceived many things during sleep that I recognised in my waking moments as not having been experienced at all. What of thinking? I find here that thought is an attribute that belongs to me; it alone cannot be separated from me. I am, I exist, that is certain … I know that I exist, and I inquire what I am, I whom I know to exist … [W]hat then am I? A thing which thinks. What is a thing which thinks? It is a thing which doubts, understands, conceives, affirms, denies, wills, refuses, which also imagines and feels … For it is so evident of itself that it is I who doubts, who understands, and who desires, that there is no reason here to add anything to explain it. And I have certainly the power of imagining likewise; for although it may happen (as I formerly supposed) that none of the things which I imagine are true, nevertheless this power of imagining does not cease to be really in use, and it forms part of my thought. Finally, I am the same who feels, that is to say, who perceives certain things, as by the organs of sense, since in truth I see light, I hear noise, I feel heat. But [sometimes it might be claimed or I might realise] that these phenomena are false and that I am dreaming. Let it be so; still it is at least quite certain that it seems to me that I see light, that I hear noise and that I feel heat. That cannot be false; properly speaking it is what is in me called feeling; and used in this precise sense that is no other thing than thinking … [P]erception is neither an act of vision, nor of touch, nor of imagination … but only an intuition of the mind, which may be imperfect and confused … or clear and distinct … according as my attention is more or less directed to the elements which are found in it, and of which it is composed …

[M]y mind loves to wander, and cannot yet suffer itself to be retained within the just limits of truth … [W]hen looking from a window and saying I see men who pass in the street, I really do not see them, but infer that what I see is men … And yet what do I see from the window but hats and coats which may cover automatic machines? Yet I judge these to be men … by the faculty of judgment which rests in my mind, I comprehend that which I believed I saw with my eyes.
Descartes, Rene. 1637. Discourse on the Method of Rightly Conducting the Reason, and Seeking Truth in the Sciences. pp. 19–20.

—. 1641 (1911). Meditations On First Philosophy. Cambridge: Cambridge University Press. pp. 14–17.

Scrutinizing “Cogito Ergo Sum”
Hyperbolic doubt is the process of doubting one’s own beliefs, or being skeptical of one’s own beliefs. This method of doubt was proposed by French philosopher René Descartes in his treatise Meditations on First Philosophy. Descartes intended to systematically doubt all of his beliefs in an attempt to build a belief system consisting of only true beliefs. Eventually, Descartes would apply this doubt to the fact of his own existence. His famous resolution, “Cogito Ergo Sum”, or, “I think, therefore I am”, was the end result. Descartes attempted to doubt his own existence, but found that his doubting proved his existence. It is impossible for one to doubt if one does not exist. This realization led to revolution of thought in philosophy and culture. However, this argument has a few areas for criticism or concern. The main crux of the problem is the assumption revolving around the “I”. The idea is that the cogito or thought itself justifies existence of an entity(in this case, Descartes). In some sense, the conclusion is an incomplete syllogism. Cogito Ergo Sum fails to assert a necessary extra premise, that whatever has the property of thinking exists. Descartes could have argued that this premise is merely self-evident(that being that for something to have the ability of thinking, there must be a thinker), and therefore not subject to his model of doubt. Logically, this makes sense, because the Principle of Instantiation states that “Whatever has the property X, exists”. If that property is thinking, then there is a thinker. For the previous argument against the cogito, this defense might serve. The extra premise is an area for contention, but the justification of the “I” is still the main issue. Perhaps Descartes should have simply stated “thinking is happening”. That does not mean that the thought occurring is the result of an entity existing. When we talk of a thought, or when we say “I’m thinking”, we’re referring to something happening from a third-person perspective. Through our experience of consciousness or our introspection, we can’t verify the existence of any third person “fact”, namely that of our own existence. You can’t objectively state something based on the content of consciousness. The mind’s subjective content doesn’t allow for a verification like that. I think Descartes’ assertion has more of a mental appeal than merit based on logical infallibility. It provokes lots of questions about the nature of objectivity and subjectivity in relation to existence, and is an interesting implementation of Descartes’ own doubt process. However, it remains an argument rather than a fact.