Plato defined knowledge at Justified, True, Belief. An idea, he said, requires all three elements to move it from mere concept to piece of knowledge.
But what makes something “justified”? This is the problem that the Philosopher Sextus Empiricus considered in his trilemma.
Sextus Empiricus
Sextus Empiricus was an ancient Greek philosopher who lived in the second and third centuries AD. He is primarily known for his works on skepticism and his writings in Ten Modes of Skepticism remain one of the most influential skeptical texts in western philosophy.
He argued that in order to claim that belief A is knowledge, it needs to be justified by belief B. So far, so simple: In order to be called knowledge, a belief needs to be justified by another belief.
But not all beliefs can justify something. A false belief, for instance, cannot properly justify anything.
So, the justifying belief must be true. And you must know that it is true. In other words: The only thing that can justify a belief is another justified belief.
So, to justify belief A, belief B must also be a justified piece of knowledge.
Now you see the problem. Each belief needs to be justified by a justified belief. And that belief, in turn, needs to be justified. Etc. Etc. Etc. …
Empiricus’ Trilemma
Sextus Empiricus thought there were three solutions to this. But that all three solutions had insurmountable problems. This is his trilemma.
Trilemma
A difficult choice between three options
I thought that the best way of representing this for you was interactively, so, have an explore:
Theory
We justify belief A with belief B, then belief B with belief C and on and on and on. Justify to infinity, and everything is, in a sense, justified.
Criticism
We don’t have infinite brains, nor infinite explanations. Just ask the world’s most informed physicist “why?” about 10-15 times, and they will say “I don’t know”. This is because we don’t have all the answers, and certainly not an infinite number.
Theory
Just stop somewhere, with a belief that cannot be doubted. Belief A is justified by belief B, but belief B is justified by Foundational belief C. That belief might be something like the laws of logic or the trustworthiness of our senses. Whatever it is, it needs no further justification.
Criticism
All beliefs can be doubted, and therefore need a justification. For instance, how do we know that logic is a decider of truth and not simply a game we play?
The justification for the Foundational Knowledge is either the thing itself (like a rational argument justifying reason) and is therefore circular, or it’s something else and therefore starts the chain all over again.
Theory
Get rid of the straight line. Consider it more like a spider’s web of interconnected beliefs, each supported and justified by the whole structure of the rest. When a new belief comes along, ask, “does this fit with my already existing set of beliefs?” If it does, accept it as a new piece of knowledge.
Criticism
At no point in the justification process is it asked “does this correspond to reality?”. We simply ask if it coheres with our other beliefs. A well-designed computer game is also internally coherent, and entirely fictional. But whilst fictional, Coherentism would conclude that it’s factual.
The Problem
If there is no way of ultimately justifying your beliefs, do you really know anything at all?
