How can we know truth? A practical guide to reality


This article presents a personal analysis and conclusions on truth and reality. It provides a foundation for determining how to separate fact from fiction.


Let’s start with a few definitions to get us off the ground:
I/me/self: we find ourselves as an individual. A mind distinct from others.
Knowledge: that which we know.
Truth: knowledge that is correct.
Falsehood: knowledge that is incorrect.
External reality: we will define here as everything external to the mind. The world, other people, the universe, anything beyond that. Although we are labelling it as real, we don’t know yet what that means. So if we are a character in a book, a figment of a god’s imagination, a computer simulation etc, this would be the truth we seek about the external reality. If a god exists, this would also be an external reality, i.e. external to our self.
Conceptual reality: this includes things that are not part of the self or external reality. We can only conceive of them within the mind. This includes for example mathematics and logic.

The self, external reality, and conceptual reality make up everything possible. We seek to distinguish the truth about these things and discard the falsehoods.

The Self

“I think, therefore I am.” or “Because I am thinking, that is something, and therefore the something that I call I exists.”  This constitutes our own fundamental starting point. We have here defined the self, thinking and existence all at once. This is a truth by definition: I am me, because I define me as the self I experience. that which I am doing I label as thinking.  I exist because I define existence as what I experience.

Not only have we found our first kind of truth: truth by definition, but we have also used experience of the self to give an origin of mathematics:
Nothing is zero, Me is one thing, 0+1=1.
We have used inference: “therefore”. This is a tool of logic and is the same as the equals sign in maths. So we have dipped our toe into conceptual reality.

Conceptual reality

Maths can be shown to be founded on logic. We can extend our logic by using more truths by definition. Here we will cover the three traditional laws of logic, which form the foundation of traditional logic.
Traditional logic concerns itself with true or false statements (propositions) and excludes other types of statements.
This makes our job really simple, because the traditional laws of logic are really laws by definition of what makes a statement a proposition in the first place:
– The rule of identity: a true statement is true, a false statement is false.
– The rule of contradiction: a true statement is not false, a false statement is not true.
– The rule of the excluded middle: there is not some other possible value than true or false.
In other words, as stated above a proposition is a statement that can ONLY be TRUE OR FALSE.

So we have logic and maths as truths by definition that can let us infer further truths, providing we start from a truth and not a falsehood to begin with. These initial propositions can also be truths by definition.

Falsehoods of the self and conceptual reality

So far, truth seems pretty easy. What about falsehoods in the realms of the Self or Conceptual reality?
Generally speaking, as we have grown and learnt the meanings of words, we haven’t spent much time rigorously defining them. There are no shortage of arguments and debates which turn out to be a simple difference in definition. We may have endless discussions about life, but it is only when we try to define life that we realise we usually only have a vague definition. So a truth by definition requires a definition in the first place. When we discuss these truths with others, we need an agreed definition.

Our ability to apply logic is also extremely poor. The mind is a cognitive miser. It takes as many shortcuts as it can. We have a large list of cognitive biases and a simple, brainless calculator is superior at maths to us. I will cover why we are poor thinkers in a later article. For now, it is sufficient to accept that we have the ability to jump to false conclusions. This means that we actually invent falsehoods from our imagination. Our imagination can allow us to reach truthful conclusions, but it can also be a source of falsehoods. A great skill of the mind is the ability to make intuitive leaps that bridge a large gap in knowledge. Here we do what calculators cannot. However the risk of false conclusions is high, and this is actually the root cause of superstitions. It explains why we invent pixies, monsters and thousands of gods.

External reality

So far we have truths that are purely subjective and internal. It is time to step outside of pure thought.
“I feel, therefore I live.” This defines living as feeling. This introduces feelings, which are internal to our physical selves, but are external to our conscious self. (We don’t directly choose them, we react to them, but also influence them in a feedback loop). We see here that feelings can be considered in the same way as the physical senses- inputs to the mind to which we can respond.
We have a large range of inputs to which the mind can respond, here is a list of 18, some of which you may not agree with. I have already added in feelings, and I also consider a sense of morality as an input (a sense of right and wrong). Whether you define these as senses doesn’t matter here- I am defining the senses as inputs to which we respond, and your mind responding to a sense of panic, guilt, pain or pleasure all fit into this category.

Some would argue that they have a sense of God. They may accept that not everyone has this sense, or they may claim that everyone has it but that many people deny it. Personally I have never felt such a sense. Whether you believe I am in denial doesn’t matter. In fact the exact list of senses doesn’t matter. What is important is the unavoidable separation between the self and any possible external reality. Our senses are our only conduit outside of the self.

What this means is that the only external reality we can know is subjective. The mind must interpret the senses, and what we discern of the outside world is therefore a model. It can only ever be a model. We cannot say that what appears as a blue wall is the reality of the situation. Taking, for example, what physics tells us about the world, the wall is mostly empty space. What appears like a single, solid barrier is a collection of  atoms generating a force field that repels the atoms in our hand with a high strength at short-range. Electromagnetic radiation in the visible spectrum does not penetrate the wall to the other side, however most of that radiation gets absorbed, whilst radiation in the blue spectrum is reflected back.

This view of physics however is, as stated, only a model. Our senses and modelling makes any “objective reality” meaningless, and anyone claiming to know otherwise is dishonest, unless they themselves can prove they are god. Our mind could be a brain in a vat, being fed signals that our mind models. Our mind could be a computer program, so that even the physical brain doesn’t exist. We could be a figment of a god’s imagination. But before we collapse in a wave of nihilistic despair, there is good news: whatever it is we map, this relative reality, is in fact a practical reality– it actually impacts us. In the words of Raymond E Feist, “Reality is what you bump into in the dark.” If you are actually a brain in a vat, but your complete experience is that a lion is ripping your limbs off, the vat is irrelevant. And so we define this practical reality as reality in the common use of the word.

If this practical reality is all we can experience, if we can never experience beyond it, then that is in fact the reality we want to understand and map. Whether we are living in the Matrix only makes a difference if we have any hope of actually detecting this- and if this happens then we simply expand our map.

Truth and falsehoods of external reality

So our problem now becomes one of accurately mapping this practical reality. Where our map correlates with practical reality we have truth. Where it does not match we have falsehood.
To find the truth we could take wild guesses, apply those intuitive leaps and just assume they are correct. But given the infinite possibilities, simply trusting the imagination with little regard for actual inputs is statistically bound to be wrong. This however is exactly what our mind wants to do- any map that helps us survive is sufficient- the end justifies the means. In fact when we have a map that seems to be working, it turns out that the mind will do its best to protect this map- it will treat conflicting information like a virus: it will stubbornly defend a false map. This results in confirmation and disconfirmation bias.

To combat this, what we need to do is recognise that our mind is a cognitive miser. That it will be lazy at logic. So we need tools that help us be systematic and logical, that deliberately doubt our conclusions. We can cross-check with the other apparent selves we find around us. So then we compare with others their map of practical reality. We define measures together to give us tools which are as objective as possible in order to compare notes. We establish a systematic method for this definition and comparison process and we title this “scientific methodology”.

We can then determine how effective this methodology has been by our ability to harness the knowledge on a day-to-day basis. If this practical reality was baseless, then this harnessing would fail. Instead we find it highly successful. Where it is not perfect, we refine our process. Once we are familiar with the scientific process, where it is properly applied, we can gain high confidence. This confidence is built on the fact that the methodology itself assumes humans cannot be trusted, and on the results we continue to see.

So scientific methodology gives us an efficient tool to refine our map, to make the map as consistent as possible with practical reality. We admit to ourselves that we only have a map, and that map is only as good as the predictions it makes. We never claim the map IS reality. If tomorrow we discover that gravity has changed, then we update our map to match.


The only truths we can really know are truth by definition, and logical extensions of this. We cannot prove a fundamental foundation for maths or logic (thanks to Gödel’s incompleteness theorem), but instead we can derive these from the fundamentals of experience of the self. Anything beyond this is not truth, but what I define as practical reality. We create in our minds a model of this practical reality based on our interaction with it. Scientific methodology using objective measurement of evidence is the tool we have shown builds the most accurate model. But we can never say the model matches “reality”, and since a model is a map readable by our brain it can never match reality. Just as a book describing a scene is not the scene. So “truth” (reality) of all that is external can never be known by a subjective being. It can only be modelled at best- which is actually all we need.


When it comes to the truth of external reality, the proof is in the pudding. This includes such harnessing of practical reality such as eating, communication, electricity and the internet. The fact that you are interacting with your senses now demonstrates that you accept this practical reality also.

About Colin Denman

"Maturity is the ability to face the truth." I seek to live a life based on reality and truth. This has led to a world view with some gaps, but as yet no contradictions. I am open to correction of my views, where gaps can be reduced and contradictions can be exposed. My writings reflect my journey and discoveries.
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