Definition of
   a priori




Definition of "knowledge"


"Absolutely certain"?


Existence of "absolutely certain", or a priori, arguments, as opposed to existence of "very probable" arguments, is not a verified belief.

Until now, no clear and trustworthy argument that has been created a priori been demonstrated.

This is seen, e.g. by the problems that are encountered when "absolutely certain" arguments, or "knowledge", should be defined.

A proposal for definition that is supported by surprisingly many philosophers reads:

Knowledge is justified true belief


The proposal can be expressed more clearly:

An absolutely certain argument is justified true belief


Several odd details are seen in this proposal:

- The term "justified" implies that is supported by trustworthy arguments. Such arguments are created through trustworthy reasoning that ultimately is based on trustworthy observations. And it is generally accepted that observations exclusively lead to probability arguments.

The definition hence claims that "knowledge" is exactly what rationalistic philosophers try to avoid, i.e. probability based.

- The term "true" is rather odd in this context. In case we were to pronounce that something is "true", as opposed to "very probable", we must have "absolutely certain" arguments about this

The definition hence reads:

An absolutely certain argument is justified absolutely certain belief


- An additional peculiarity is that the proposal often is claimed to be a citation from Plato's Theaetetus [Chisholm, Williams, Rescher]. This is claimed in spite of that Plato in this text clearly expressed that knowledge cannot be this:

And so, Theaetetus, knowledge is neither perception nor true judgment, nor an account added to true judgment

Plato - Theaetetus, 210b

- And, finally, the definition has been falsified using examples demonstrating that it cannot be correct [Gettier].



Philosophers often have trouble to clearly define what they really discuss.

Is it possible that the definition is about our everyday use of the term "knowledge", which at this website is called "very probable" arguments?

Probably not, as the term "true" discloses that it aims at "absolute certainty".


Definition of common speech "knowledge"


According to above, the definition of the term "knowledge" becomes untenable in case it is assumed to denote rationalistic philosopher's "knowledge", i.e. "absolutely certain" arguments.

On the other hand, the definition using a similar expression becomes correct in case it describes "very probable" arguments, i.e. what in common speech is called knowledge:


A "very probable" argument is justified belief


As mentioned above, the term justified implies something that is ultimately based on perception.

Chisholm 1989 - Theory of Knowledge 3Ed, p.90.
Gettier 1963 - Is Justified True Belief Knowledge? Analysis 23, p.121-123.
Rescher 2003 - Epistemology, p.369.
Williams 2001 - Problems of Knowledge, p.26.