What is Truth?–The Cartesian Answer and Rebuttals

An attempt at answering humanity’s (arguably) most important question through the lens of a 17th-century philosopher

Mukundh Murthy
8 min readNov 20, 2020

An Introduction to the Classic Descartes Story

What if everything that you’re seeing in front of you is completely false? Sounds absurd, but the truth is, there’s no way to deny it. You could be dreaming, or maybe we’re in some sort of simulation where we’re being programmed to think in certain ways. Again — these thoughts are quite absurd. But, there’s no way to absolutely prove or disprove these ideas, and that’s why we can’t put them aside. This is the way that René Descartes, a 17th-century philosopher, mathematician, and natural scientists started questioning everything that he thought or believed. He saw his beliefs and logical views of the world as a bag of apples, where one rotten apple (false belief) could contaminate the rest. In order to keep his apples pristine, he would need to dump out all of his apples, and then re-evaluate each apple, put all of his effort in trying to prove that the apple is rotten, and then after all of the efforts, if it proves to still be pristine, add it back into his bag.

He really struggled with this, as he questioned everything. Everything. He completely threw away information gained through sensory experiences and that left him with very few thoughts left to validate. Then one day, he had his aha moment, and came up with his favorite Cognito argument: ‘I think, therefore I am.’ He realized that we cannot doubt that we doubt when we doubt. In other words, the act of doubting itself proves the existence of a subject that is doing the doubting (at least, that’s what he thought, more personal interpretation on this later :-)). This stood as the first pristine apple in his new bag, an argument that stood as a metaphysical pillar that could not be destructed. And this was truly the start of his legacy. A legacy that’s reached out centuries ahead to where we are now. He went on to use this basic proven axiom as support to many other of his deductions, including the existence of God (highly controversial as we’ll see later on).

That was a high-level view of Descartes and what he stood for, but there are much more complexity and richness to his philosophical identity than his Cognito argument. Underlying his derivation of the Cognito Argument was a desire to define — in a metaphysical sense — truth.

When we talk about truth alone, we talk about the absolute truth, the global truth that is invariant to our emotional biases and information that is temporarily available truth. The metaphysical truth defines the fundamental nature of reality, not one inside our heads, and this is where I believe Descartes's conclusions go a little astray.

In understanding how Descarte’s defined truth, we need to understand a couple of components of his thought process.

  1. Conclusions derived from the Pure Intellect vs Sensory information
  2. The Mark of Truth
  3. His proof of God and the Cartesian circle and rebuttals

Intellect vs Sensory Input: How humans construct knowledge about the world around us

Before I can get into Descartes’s views and my own criticisms, we need to understand the different kinds of knowledge that exist.

  • General principles of physics – This type of knowledge concerns physics as in ‘metaphysics’: what are fundamental unifying laws to the world around us, that are independent of any particular subject or domain. It concerns topics such as being, knowing, space, and time.
  • Natural phenomena, theories, and laws: Properties and fields such as optics, magnetism and gravity.

While we intuitively think that most of our understanding comes from the sensory information available to us, Descartes believed that our ‘pure intellect’ plays a larger role, both for understanding general physics and natural phenomena, but more so for general physics.

So what’s pure intellect? To understand this, we must examine Descartes’s ontology. An ontology is a framework used to construct and interpret the world around us. In Descartes’s ontology, there exist three main components: mind, matter, and god. According to him, mind is composed of intellect (which is made of pure imagination, pure intellect, and sense perception) and will (which is made of desire, aversion, assertion, denial or doubt).

Think of pure intellect and pure imagination as insights that stem from within the human mind, that aren’t derived from any visual or auditory input. The will is what looks at the different interpretations that we construct and judges them. It’s the part where we judge ourselves based on what we believe. Sometimes, we may be uncomfortable with what we believe, and we may deny it, and other times may assert it as it confirms something that we already believed.

Anyway, Descartes believed in the pure imagination and pure intellect, components independent of our sensory experiences, that contribute to the majority of our thoughts. The essence of the human mind. That’s why you could often find Descartes’s in bed, lying down and doing nothing but thinking. Though his view on this changed throughout his lifetime, he didn’t see the value in huge scientific apparatus’s to generate insights, when we already have our own minds as supercomputers and machines to generated superpowered insights.

The Mark of Truth

Here’s what we’ve been waiting for: Descartes's definition of truth. He defined it as ‘a clarity and distinctness of thought’ after trying to forcefully validate your ideas as much as you can. In other words, take an idea that you have, distance your sensory self from an idea, leaving it in the hands of your pure intellect, and try to disprove the idea with all of your energy. If the idea still stands, you are entirely resolute, and the idea doesn’t feel blurry in your head, there you have it: you’ve achieved truth according to Descartes. But there stands one major caveat…

Just because humans are ‘clear and distinct’ in thought, doesn’t mean that we’ve reached the truth… What if we’re subconsciously biased, and we’re remembering what we choose to remember, thereby aiding our own biased thought through confirmation bias? Or what if we don’t have the information? In Daniel Kahneman’s book Thinking Fast and Slow, he describes an abbreviated principle called WYSIATI — what you see is all there is. Since we can’t see everything and what we see is all there is, is it fair to say that just because we are entirely confident in our idea, that it is the absolute truth. An example of this — we can look at Descartes’ Cognito argument. He said I think, therefore, I am. However, he does not define existence and is confined to his own definition. If entities in virtual simulations could have thoughts and feelings, they might exist to themselves, but not to the outside world. This is where I believe Descartes has fallen prey to WYSIATI.

Ultimately, though, Descartes did find a rebuttal to rebuttals like mine, albeit a very controversial one.

The Existence of God

Here’s a simplified version of Descartes’s proof of the existence of god.

The universe is infinite, therefore there must be an infinite being behind the creation and supervision of the universe.

Descartes’s definition of God, is somewhat finicky, as he seems to manipulate god and use it as a filler to fill gaps in his ideas.

For example, let’s start off where we ended the last section. Why can trust ‘clear and distinctive’ judgment from humans as a measure of absolute truth? According to Descartes, this is because God exists, and God has already implanted true ideas in our heads. Ok, let’s just say this idea makes sense so far.

But now comes WYSIATI. Why do humans make errors in our judgment when we might already have this divine intuition in our heads? Here again, Descartes seems to use God as a filler. He says that ‘God was working with the finite mechanisms of the human body.’ This is quite literally a paradox. If God is infinite, why would God create a limited human body which makes it harder for God to make sure all humans are moral and make correct decisions?

Though I’ve phrased the paradox based on the principle of WYSIATI, other variations of the paradox have come to be known as the Cartesian Circle. A loop of thoughts which can never be logically exited.

Here it is: Truth is defined when humans believe something with clarity and distinction. Truth can be defined this way because God has planted these ideas in our head. How do we know that God exists; because we believe it clearly and disinctively. How do we know that believing things clearly and distinctively equals truth? Because God exists. How do we know that God exists?… And so on….

I hope this article has provided you with an engaging excursion through Descartes’s thought processes and his Cognito deduction. However, at the end of the day, there are flaws in his argument that are yet to be clarified — which, really, if you think about it, may never be resolved.

Here’s why. If you really think about it, Descartes entire argument is founded on the statement below:

The human intellect is reliable because it was created by god

His logical deductions that follow are rendered invalid since this initial conclusion itself is not entirely justified.

There is no absolute truth. What each person, society, or nation defines as truth is the function of the religious, cultural, and time-based beliefs of the group of people.

I personally believe this. It’s not completely justified, but it serves as my framework to think about truth in the world around me until I completely justify one.

This view is not nihilistic. It just says that there may be local truths, local to a specific time, place, or groups, but global metaphysical truths may not exist and we must come to terms with that. Different global truth frameworks may serve different purposes and utilities in different situations, but nevertheless, there might never be one that we can declare is the absolute truth–until we can prove that the human intellect is not flawed.

Hey! I’m Mukundh Murthy, a 16 year old passionate about the intersection between machine learning and drug discovery. Thanks for reading this article! I hope you found it helpful :)

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Mukundh Murthy

Innovator passionate about the intersection between structural biology, machine learning, and chemiinformatics. Currently @ 99andbeyond.