Today I was arguing with my friend that the colour of sky is subjective.

I claimed that the colour of sky is a subjective idea and a person who is colour-blind may perceive it as a different colour. They replied the following:

The sky may be blue for you but brown for a colour blind person, however that does not change the fact that it is blue

I thought about it a bit and said

For the example of colour blue, that is a result of how the brain processes the electromagnetic signal hitting the eye. It maybe possible to have another alternate mechanism to process electromagnetic wave which maps that specific frequency of light hitting your eye to be perceived as another colour. So, really there is no objective truth other than maybe measuring the exact frequency of that light (which is not to perception).

But, after writing this, I came to bit of a worry. I found it quite scary that there may perhaps be no objective truth in this world at all.

What may be arguments to refute the idea I replied with? What are philosophers take on the matter if any idea can be subjective?

For reference, here are the definitions of subjective and objective from the dictionary:

Subjective: based on or influenced by personal feelings, tastes, or opinions.

Objective: (of a person or their judgement) not influenced by personal feelings or opinions in considering and representing facts.

  • How the brain processes the colour blue is just how the brain processes the colour blue. The existence of blue doesn't (necessarily) depend on this and how you perceive it doesn't have to correspond to what blue "actually" looks like. Although that touches on the core of the issue: you can't conclusively determine whether blue actually exists because the world passes through your subjective perception before you get to reason about it. Here's probably also an element of the psychology of how different people perceive colours and whether colours exist in the physical world or just in perception
    – NotThatGuy
    Commented Jun 14, 2021 at 12:39
  • "Although that touches on the core of the issue: you can't conclusively determine whether blue actually exists because the world passes through your subjective perception before you get to reason about it" Exactly @NotThatGuy
    – Babu
    Commented Jun 14, 2021 at 12:47

6 Answers 6


You are correct, in that as we define the terms, a knowledge of a perfect objectivity is not possible. And to be pedantic, even what you refer to as the "electromagnetic wave" is not proven to be perfect objective knowledge. To make a colourful example, people thought Sommerfeld's adjustment of Bohr's atomic model was correct (Electrons as tiny balls), but it was proven wrong.

Physical theories qualify as scientific if they are testable, and stand unless they are found to be falsifiable. But they are not ultimately provable.

The objective electomagnetic energy reality would be a Kantian thing-in-itself, dismissed by Nietzsche thusly:

The Will to Power, 558

The thing-in-itself is nonsense. If I think all the "relations," all the "qualities" all the "activities" of a thing, away, the thing itself does not remain: for "thingness" was only invented fancifully by us to meet certain logical needs—that is to say, for the purposes of definition and comprehension (in order to correlate that multitude of relations, qualities, and activities).

We see the appearances of reality, which we call phenonmena, but of any reality beyond - the noumenal thing-in-itself - we see nothing.

Even of the foundation of human life and consciousness - the being of beings - we see nothing.

But that is as we define the terms. If we change the definitions there is more scope, e.g. Rusi-packing-up's comment here

In dreams of a spirit seer Kant more directly (than CPR) describes the noumenon as knowable mystically thanks to his encounter with Swedenborg repository.hkbu.edu.hk/cgi/… but these matters are hardly knowable(!) to me


If we consider the example of the sky being blue, then the color is subjective. Blue in the sky is not there if no one looks at it (just as the sound of a falling tree is not there if there is no one to hear it). Light coming from the sky, the sky itself, the sun, etcetera, are all objectively existing things. The wavelength of electromagnetic radiation is an objective feature. It happens to go along with a blue experience.

So while many subjective experiences are there that won't be there if we are not there (colors, sound, sense impressions like heat, cold, or an itch), there are also many objective features of reality (wavelength of EM radiation, the EM field itself, soundwaves) to which have no direct access to with our senses but only by our thought. Thought is a subjective feature also, so the objective features and the subjective ones are tightly bound together.

As you said, if another physical process would give rise to a different experience of the "blue" wavelength it could be that two different people see a different blue (if you rub one eye the colors seen by both eyes are slightly different). You can call both blue but the subjective experience is different. You can call the wavelength the thing that is the same for both and it is the same indeed for all people (that's why it's called objective). But that wavelength thing is again a thing that's the result of thought and as such subjective. Objective reality and subjective reality are intertwined to a high degree, if not completely. There is no such thing as purely objective or purely subjective.

  • On further thought, the wavelength of light is also subjective at least as we know it. It may exist in the world without us, but to detect it, we have to perceive it and run the measurements of it through our brain and as soon as this happens, any hope of objectivity goes down the drain IMO
    – Babu
    Commented Jun 13, 2021 at 23:57
  • Using an apparatus to measure is just keeping a middle man between the brain, sample problem still exists
    – Babu
    Commented Jun 13, 2021 at 23:58
  • @Buraian That's why I Wrote that subjectivity and objectivity are intertwined to a high degree if not completely.
    – user52804
    Commented Jun 14, 2021 at 0:07
  • @buraian a big difference between our perception of blue and the measure of wavelength is, while I can't share my feeling of seeing the blue sky with you, I can show you the wavelength sensor and the number it outputs. We can discuss how the sensor work, marshall it against other colors, make a list of the assumptions that go with our measurement (for example, that the sensor works as intended, etc). Our feelings are internal, but the sensor is external to both of us, and we can agree about it. That is what makes it "objective".
    – armand
    Commented Jun 14, 2021 at 1:19
  • @armand The problem is that the sensor was created by a person by subjective thoughts and not someone god who is objective. Now, as soon as the person who created the sensor calibrates the device, he immediately includes his biases and there is no objectivity anymore
    – Babu
    Commented Jun 14, 2021 at 9:38

Tell your friend about tetrachromacy Some humans see a 4th primary colour. More on colour here: Could color be a fundamental thing about the universe?

The lack of objective truth is like the lack of a central processor for the internet - we have a host of interactions and propagations of information, and negotiate reality, including with ourselves.

It's not 'truth & reality are purely up for grabs' though. We have tools, like consilience eg if all our senses agree, then we take something as far more likely to be real, and if they disagree we expect an optical or other illusion.

Our brains do a great deal of work 'behind the scenes', to clean-up and integrate data as it comes in. See Anil Seth's 'Your Brain Hallucinates Your Conscious Reality'.

Scientific consensus doesn't prove objective reality. It is tentative truth, subject to revision, and affected by social & cultural dynamics. But it's better than asking a random person at a bar. Lack of objective reality, doesn't mean all subjective realities are equally valid. Science isn't a democracy either, it's about reasoning and evidence, and unpopular ideas have often proved correct.

The replacement for objectivity, is not subjectivity, but intersubjectivity. See this post for a refutation of solipsism on that basis, & more about intersubjectivity: Is there anyway to prove things happen/exist if I'm not aware of them?


The objectivity of knowledge has been a mainstay of philosophy since forever. The most famous related ancient concept is Plato's Cave (not the most similar one, but a good starting point):

In the allegory, Socrates describes a group of people who have lived chained to the wall of a cave all their lives, facing a blank wall. The people watch shadows projected on the wall from objects passing in front of a fire behind them and give names to these shadows. The shadows are the prisoners' reality, but are not accurate representations of the real world.

Source: Wikipedia

Plato's "belief" was that there were multiple higher 'levels' that were increasingly more objective where all things in the real world have an ideal Form or Idea that exists outside our reality. So Plato's explanation would be:

We call both the sky and blue jeans by the same color, blue. However, clearly a pair of jeans and the sky are not the same color; moreover, the wavelengths of light refracted by the sky at every location and all the millions of blue jeans in every state of fading constantly change, and yet we somehow have a consensus of the basic form Blueness as it applies to them. Says Plato:

But if the very nature of knowledge changes, at the time when the change occurs there will be no knowledge, and, according to this view, there will be no one to know and nothing to be known: but if that which knows and that which is known exist ever, and the beautiful and the good and every other thing also exist, then I do not think that they can resemble a process of flux, as we were just now supposing.

Plato believed that long before our bodies ever existed, our souls existed and inhabited heaven, where they became directly acquainted with the forms themselves. Real knowledge, to him, was knowledge of the forms. But knowledge of the forms cannot be gained through sensory experience because the forms are not in the physical world. Therefore, our real knowledge of the forms must be the memory of our initial acquaintance with the forms in heaven. Therefore, what we seem to learn is in fact just remembering.

Source: https://en.wikipedia.org/wiki/Theory_of_forms

The valuable thing to note here is that this type of thinking will by necessity touch upon one's beliefs about reality at a very fundamental level. About the relationship between oneself and the reality one may (how can one know there is a reality out there?) inhibit.

Obviously there are many other ideas about the nature of knowledge. This branch of philosophy is called Epistemology and to say it's a 'controversial' field (in the sense that everyone has their own ideas/beliefs) would be an understatement. The idea that one can't know about anything for sure outside the existence of their own mind (closest thing I could think of to what you were describing) would be Solipsism which dates back to a couple of centuries BC and states

Solipsism was first recorded by the Greek presocratic sophist, Gorgias (c. 483–375 BC) who is quoted by the Roman sceptic Sextus Empiricus as having stated:

  • Nothing exists.
  • Even if something exists, nothing can be known about it.
  • Even if something could be known about it, knowledge about it cannot be communicated to others.

Much of the point of the sophists was to show that "objective" knowledge was a literal impossibility.

Source: https://en.wikipedia.org/wiki/Solipsism

Which can be a useful starting point in looking at why most people reject this theory. There is no way to directly falsify or reject such a position, but there is solace in the fact that virtually all reject this theory, as at the end of the day there are few (if any) people who just stop interacting with the physical world because they don't believe it exists. So instead the question becomes: "How does one belief that one can derive objective knowledge?". Personally I hold to the idea that there is an unobtainable objective truth 'out there' and all we can do is try to approach it. If you want to explore all the different positions I would recommend just opening https://en.wikipedia.org/wiki/Epistemology#Schools_of_thought_in_epistemology and see you in a couple of years 😅

  • This was a great answer, I didn't understand it when you originally posted it.
    – Babu
    Commented Mar 20, 2022 at 10:09
  • @Buraian Any advice how I could've communicated/explained the concepts more clearly? Commented Mar 20, 2022 at 11:20
  • I think one point is that, suppose you have a well written answer, then the person who is reading it must be receptive to understanding the well written-ness. One more point is that the answer to some degree is unfocused. It presents it self as a sort of survey rather than a 'bullet' or sort going straight to the question. Survey's are great in itself but as mentioned earlier, one needs some exposure iwth basic ideas to understand it.
    – Babu
    Commented Mar 20, 2022 at 11:27

I would argue that all thoughts are objective, if phrased correctly:

The information from my eyes about photons with a certain wavelength, correspond to my personal definition of blue.

I don't see any room for subjectivity in that.

However, we cannot objectively convey these thoughts to other people. Because my definition of blue differs ever-so-slightly from your definition for blue (this is true with every word and idea).

So while thoughts may or may not be objective in your head, they cannot be objectively stated or written down. Information will always be interpreted in a different way, with a different meaning, than was intended.

  • Consider the dictionary definition I have taken ni the post "Objective: (of a person or their judgement) not influenced by personal feelings or opinions in considering and representing facts.", if it varies from person to person, then at least according to this definition, it must not be objective
    – Babu
    Commented Jun 14, 2021 at 11:20
  • With that definition, nothing that a human ever thinks or says can be objective, because we have our own private dictionary in our brains that are ever so slightly different.
    – Tvde1
    Commented Jun 14, 2021 at 11:51
  • However I think it is ""true/objective"" to state that a piece of information corresponds to the definition of my private dictionary.
    – Tvde1
    Commented Jun 14, 2021 at 11:52
  • What I mean to say is I don't say "4 people live in my house", I say "4 people live in the house @Tvde1 lives in". The second variation can be exclaimed by everybody, while the first variation contains a relative reference ("my house" refers to something else depending on who says it)
    – Tvde1
    Commented Jun 14, 2021 at 11:54
  • "my personal definition" isn't subjective..? You seem to be talking about the quale of a specific personal colour experience - archetypally subjective.
    – CriglCragl
    Commented Jun 14, 2021 at 11:57

Color perception is a bad example, as it depends upon the perceiver, and is therefore a subjective truth.

A better example would be "A molecule of oxygen gas is composed of two atoms of oxygen, connected by a covalent bond." This is an objectively true statement.

The statement does not depend on the observer (hence it is objective). It is true, on the basis of all scientific investigation up to this point. Only extreme skepticism would deny this to be true. If, for some reason, it is actually false, the statement would still be objective (not depending on the observer) but false.

If you consider the use of science to be a bridge too far, then use the statement, "One apple plus one apple is two apples." This is based more in math and primitive observation, and is again objectively true.

  • Hi Matthew! The example of the oxygen molecule, I'd say, has some flaws. To describe to be in such and such way , we must take information external to us and run the process of our mind to conclude about it's structure. I think a better explanation of the current point was the first comment on my post. And you say that scientific investigation suggests objectivity but I disagree to that too because scientists find they are wrong and amend their mistakes all the time. It is no authority but rather mutual agreement that science does work (independent of it producing practical results or not)
    – Babu
    Commented Jun 15, 2021 at 11:13
  • 1
    The level of skepticism you describe is unlivable. To reject truths that all investigation reveals to be true leads to fatal conclusions. You must reject facts like food is good for eating, because nothing can be proved. Then you starve to death because you don't eat. I hold as axiomatic that unlivable philosophies are false. Commented Jun 15, 2021 at 16:39

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