Knowledge: True belief based
1. To provide a
definition of "knowledge" that covers all cases where it is used sensibly is
somewhat difficult, since one knows one may believe that one knows and may later find out
that one was mistaken, even while having evidence that supported one's belief, and one's belief that with that evidence one knew.
Now... that one knows one may believe one knows and
later find out one was mistaken is a true belief about claims of knowledge for which there is a
lot of evidence, and so it seems one knows at least one may be mistaken.
Consequently, it follows there are some things one knows, in the sense given,
and that is a useful starting point.
Also, besides knowing one may be mistaken, there is the more positive fact
that in order to express skepticism one must at least know some language to
claim in it - inconsistently - that one doesn't know anything.
Furthermore, in the same connection - related to skepticism - it seems
evidently true that there are many things that one does not know, and so it
follows that one also knows that there is much one does not know,
which is an instance of the truth about knowledge just established, and indeed
also is one of the firmest certainties and best pieces of knowledge that a human
And it is important to remark that True belief based
on evidence - knowledge - comprises true belief
in probabilities based on evidence, where the "true" in "true belief" refers to
axioms of probabilities and statements of fact.
Therefore it is entirely possible that one's true theoretical beliefs, that
imply things beyond one's experience, comprise only probable contingent
statements and no certain ones, though one requires certainty for statements of
2. To consider knowledge in some more detail, it makes sense to
distinguish three kinds of - presumed - knowledge:
1. Practical knowledge
2. Empirical knowledge
3. Theoretical knowledge
Practical knowledge is knowledge of how to do things, and so
relates to action and abilities. Thus, in this sense one may know how to cycle,
may know how to differentiate, and may not know how to make a pizza.
It is an interesting fact about practical knowledge that one may know
perfectly well how to do something, and can prove so by doing it, while one is
at loss to give a good explanation for it. The ability to cycle is one good
example: It is neither easy nor does it make much sense to explain how to do
this in words.
The way to establish whether someone has a certain kind of practical
knowledge is to find out whether they can do the things they may claim they can
do. Incidentally, one may know how to do things - such as speaking in prose, as
the proverbial French Mr. Jourdain, of Molière - that one may not know that one does.
Empirical knowledge is knowledge of such facts
as one may meet in experience. These are
always particular and may be of many kinds, including such as need a lot
of training or some apparatus to experience them.
Also, a lot of empirical knowledge one has was in fact conveyed by teaching,
and comes from authorities, but may be all the same quite reliable and true. And
it often is a bit vague what is empirical. Thus, one may have been in
England, and thus believe one has empirical knowledge about England, but even so
meeting in experience what is represented by the term "England" is a bit too
much for personal experience, although one may have a lot of knowledge of the
English landscapes and people. (See:
The way to establish whether someone has a certain kind of empirical
knowledge is to somehow test it, either using logic
and by reference to other knowledge one believes one has, that may imply or
refute it, or by some sort of experiment, which may be as simple as looking up a
word in a dictionary, or as complicated as using a cyclotron or PET-scanner.
Theoretical knowledge is knowledge of such
facts as are represented by theories that
include theoretical terms.
Theoretical knowledge tends to go beyond
experience, if only for the reason that empirical theories that do not make
predictions about future experiences - which does not exist now - cannot be
Many of the vagueries and problems with the term "knowledge" concern
theoretical knowledge, for the reason mentioned above: One knows, also about
science, that one may have been quite justified to believe that one knew
something, at least in the sense that it was far more probable than not, and
even so it turns out that one was mistaken.
One of the things that is often missed in discussing these problems is that
even if a theory is mistaken in the sense that it logically implies something
that is not really so, even so the theory may be and have been quite
Indeed, one real test for scientific knowledge, that also
distinguishes real scientific knowledge from the claims of faith of any
kind, is that it can be used to produce technology that works in practice
whatever one believes or knows about the theories on which it was based. (Thus,
the faithful of some religion may murder their opponents with weapons that
cannot exist if their faith is true, and would not have been developed by
members of their faith.)
And all scientific knowledge, whether or not it will keep standing in the
future, that has led to some technology that would not have existed without it,
must be adequate at least in that respect.
The way to establish whether someone has a certain kind of theoretical
knowledge is to somehow test it, either using
logic and by reference to other knowledge one believes one has, that may
imply or refute it, or by some sort of experiment of whatever empirically
testable deductive consequences of the theory.