Every day we take the world around us for granted. We accept our perceptions as axiomatic certainties upon which everything we know is built; yet this foundation is a lie. Through the toil and focus that daily life demands, one never stops to reflect or contemplate. The Enlightenment philosopher, René Descartes did stop to reflect. Descartes did this through his meditations in which he attempted to grapple with the certainties of the world. In his writings, Meditations on First Philosophy, Descartes considers the idea that “some evil mind, who is all powerful and cunning, has devoted all their energies to deceiving me. I will imagine that the sky, air, earth, colours, shapes, sounds and everything external to me are nothing more than the creatures of dreams by means of which an evil spirit entraps my credulity” (First mediation) Through this fascinating thought experiment, Descartes highlights how we cannot know for certain even our most basic assumptions as much as they seem evidently genuine. 


The reason one cannot trust their senses is hardly an argument as much as it is a rebuttal to the claim that the senses we perceive correlate to things external to us. This could be considered the fallacy of induction: one thing does not necessarily follow the other. The emphasis is on the word ‘necessarily’ - it seems to us, in all likelihood, that our sense do in fact correlate to external things, but this does not have to be the case. It would not be contradictory for it to be otherwise; we would simply be mistaken in the assumption that what we perceive exists beyond our minds. The main argument one may immediately propose against this is that our senses seem to consistently correlate to things outside of us, but all that is really saying is that there is no inconsistency in what we perceive. This is irrelevant to whether what we perceive to be beyond us truly does exist because there is no mode by which we can know of the external world except through our senses which, as established, do not necessarily have to be accurate. Our senses are deceived in minor ways all the time: optical illusions, the distortion of memories, seeing faces in obscure objects and patterns and so on. There is even a blind spot in the human eye where the optic nerve passes through the surface of the retina, yet one does not notice this because the brain processes the sensory information and fills in this blind spot. Stepping back, we can see just how malleable and easily deceived our sense can be, even if in minor ways. One cannot prove that everything is an illusion. 


Given this logical uncertainty, Descartes considers what we can know. He draws parallels to “Archimedes [who] looked for only one firm and immovable point in order to move the whole earth;” (Second meditation) and Descartes finds this through his famous saying “Cogito ergo sum”. The saying translates to “I think therefore I am” - it argues that the only thing one knows for certain while they are thinking is that they exist. Descartes elaborates “I am, I exist; that is certain. But for how long? As long as I think, for it might possibly happen if I ceased completely to think that I would thereby cease to exist at all.” (Second meditation). The reasoning behind “Cogito ergo sum” is simple upon reflection: it is not possible for nothing to think; being is a prerequisite to thinking. Therefore, since to think is something that truly exists while being experienced, then while one is thinking they know that they are doing so, and from this they can logically, and without flaw, conclude that they must exist. This cannot be done to prove that others exist, because one does not truly know if others are thinking, only that one perceives them to think. Yet one knows themself when they are truly and genuinely thinking. 


Given this information, how should we then respond to this in our daily lives? This extreme level of doubting seems unhelpful in our daily lives given the impact our perceptions have on our wellbeing, whether they are illusions or not. In one sense, it does not even matter, since they affect us all the same. If anything, perhaps this article made you think and consider the remarkability of our senses, the fact that despite having such a wealth of knowledge about our world, we still know so little about even the fundamentals. We can all be grateful for existing, because as you read this article and think about it, you most certainly truly exist.