René Descartes was a French philosopher, scientist, and mathematician. Also known by his latinized name Renatus Cartesius. He was born in France on 31 March 1596 and died on 11 February 1650 because of pneumonia. He is a Primitive figure in the emergence of modern philosophy and science. He connected two separate fields of maths, geometry, and algebra into one, analytic geometry. 

Around his 50s, he was at Netherland. A night of 1640 in Leiden, he picks his pen… “I am here quite alone,” he continues, “and at last I will devote myself sincerely and without reservation to the general demolition of my opinions.”

Any better way to spend a night?

But he had quite a reason: as a mathematician, he always thinks about the knowledge, if its foundation is not solid it will doom to collapse. So, he underlines that if there is a reason to doubt something, no matter how thin that is; it should be considered as false.

What is true?

Now having this rigid criterion in his mind, it was not long before he struggles to feel that anything is real. Even he himself.

The way we dream and hallucinate, for Descartes it was simply untrustworthiness of our senses. Indeed, sometimes we dream something that seems to be real. Sometimes we hallucinate to extent even we cannot imagine. Sometimes we see things happening in some different ways than others. 

When our cognition of the world is different it creates a dispute. We think that we are right, we are correct and when we prove false, at first it feels like our ego is hurt. We think that our understanding cannot be wrong. And eventually “Is it real the way I feel this world?”

But as the Descartes’s rigid theory on truth outlined above. Where we stand? If our experiences can be doubted? Then it is enough to declare it as unreliable or even false. That our senses are sometimes misleading us without our knowing or maybe all the time.

Consequently, if we cannot trust information from our own senses, then how can we confirm existence of anything?

Maybe we are living in a Matrix. Where our brains are connected to a computer and all the things, we are experiencing is a mere simulation, or maybe nothing even exists, all of this is our hallucination, everything is an illusion. A part of the mental realm, or maybe a thought someone have putted inside our brain. To mislead us from the reality of the eternal.

Can we ever certainly say that, yes, everything we feel, we experience, is a reality. 

Not just our sensory capabilities, but what if our ability to think, to redress, is also impaired. If we have redressed incorrectly before than how will we ensure that we are redressing it correctly now? Descartes notes.

May be 2 + 2 is equal to 5, not 4, and someone have filled your mind that it is 4.

Then he got himself in a right state over all of this:

"So serious are the doubts into which I have been thrown as a result of yesterday’s meditations that I can neither put them out of my mind nor see any way of resolving them. It feels as if I have fallen unexpectedly into a deep whirlpool which tumbles me around so that I can neither stand on the bottom nor swim up to the top."

Overwhelmed with the worry, he seeks to repair some of the damage caused by his thinking of something, anything, we are certain of, that it is true.

I think, therefore I am

A clearer translation of Descartes’s definitive statement might be, “I am thinking, therefore I exist.” Regardless, in his profound declaration: cogito ergo sum! Descartes assures himself of his own existence.

Descartes believed his discovery of the Cogito to be hugely significant, for it withstands all the scepticism we can throw at it.

Indeed, even if we doubt the reliability of our senses, or even we doubt the reliability for our reason. The Cogito remains true. For how wrong we can be in our estimation of reality we can never be wrong about the fact that we exist. In order to think about something wrong or right, I must exist.

This way, Descartes establishes the base, a solid foundation for certain, an undoubtable knowledge that: A thinking mind must exist.

So, in his Meditations on First Philosophy Descartes attempt to rebuild all human knowledge and establish proof for the existence of among other things, God.

As, he demolishes our confidence about existence of anything but our thoughts. Descartes, creates two separate realms, the mental and physical. The mental, we can be sure exist, but the physical world needs to somehow to be linked to it.

Till today, philosophers are trying to bridge this explanatory gap.

On the request of Queen of Sweden, he moved to Stockholm to teach her philosophy in 1649. The queen was an early riser which was contrary to Descartes. He preferred to sleep late which he was practising from his college time. As he started to rise 5:00 AM in the morning, his health started to deteriorate. He caught pneumonia which later caused death.

His legacy was the search for truth. The concept of rationalism he brought was to find the true knowledge using the power of reasoning and senses. He uses mathematical logic and reject the belief in empiricism of Aristotle. His idea of searching truth through our own ability to reason remain the central idea of philosophy for more than 300 years. He inspired philosophers like Spinoza and Leibniz. Apart from philosophy his writings in geometry inspires Newton and Leibnitz. In Descartes’s Bones, Russel Shorto wrote:

"Thus, the essence of Cartesianism - its philosophical kernel, which encompassed more than science - not only lived on but expanded into virtually every corner of human life, evolving, and adapting and spawning new generations"

While some of Descartes' ideas have been discredited, his influence on both philosophy and science cannot be denied.