What is called "knowledge" can be either practical or propositional. Practical knowledge is 'knowledge-how', whereas propositional knowledge is 'knowledge-that'. In the context of the concept of truth we shall only be concerned with propositional knowledge. In a broad sense a theory of truth should include a theory of (propositional) knowledge of what is true, or a theory of what we know to be true. Similarly, a theory of relevancy should include a theory of (propositional) knowledge of what is relevant, that is, of what we know to be relevant; and a theory of property a theory of (propositional) knowledge of what is someone's property, that is, of what we know to be someone's property. Whether a theory of knowledge of what is relevant, and of what is property, is simply part of a theory of knowledge of what is true is itself an issue for those theories.

Propositional knowledge is true belief, but true belief need not be knowledge, because a belief may just happen to be true. If someone believes that it will rain at a particular moment in the future, and it does indeed rain at that moment, 'er belief is not knowledge or has not been knowledge for that reason. What distinguishes such a lucky guess (if it is one) from knowledge is at least justification, epistemic justification to be precise. But even this standard definition of knowledge as justified true belief has been attacked for being too simple. Traditionally its criterions are: (1) p is true; (2) S believes that p; and (3) S's belief that p is justified. It has been argued that these three criterions are minimal ones, and that S should also not believe that p, if p is not true. Moreover, S should indeed believe that p, if p is true. On such a conception of knowledge it is said to 'track', as it were, the truth that p. For our present purpose, however, it is not necessary to consider such additional criterions. The first step, that is, the one from true belief to justified or grounded true belief is the most important one for us here.

The central problem for those interested in theory of knowledge is, of course, whether something can ever be known for sure, and if so, how. If something cannot be known for sure, the problem is whether one can still be justified in considering something true nonetheless. Extreme skepticists would say that one cannot know anything for sure. They doubt everything. Dogmatists, on the other hand, claim knowledge without ever seriously and honestly examining what their claims are based upon. They do not doubt their 'truths' which they may readily call "self-evident truths" or "revelations". (Such 'truths' which are mere products of belief we shall henceforth call "doxastic truths". As a product of belief a doxastic truth need not be false: it may happen to be true.)

Skepticism admits of degrees. A skepticist may only doubt certain kinds of belief, or specific opinions regarded as knowledge by others. 'E may be skeptical about the 'apriori intuition' or 'knowledge' of a rationalist, but also about the 'empirical intuition' or 'knowledge' of an empiricist. Rationalism in the epistemological sense, or apriorism, is, then, the view that there is knowledge which does not depend on experience for its justification, knowledge which can be derived from 'self-evident' axioms or principles by deduction. It is also called "rationalism", because this knowledge is said to come from reason or from ideas the mind would be endowed with independently of any experience. The complement of apriorism, empiricism, is the view that all knowledge depends on experience for its justification. Sense perception and introspection are the sources of empirical knowledge which can be derived from those sources by induction.

Both apriorists and empiricists may consider themselves skepticists, or may start as such, the former ones with regard to empirical knowledge, the latter ones with regard to apriori knowledge. The apriorist may show how people can be deceived by their senses, and tell us that we cannot be certain that this does not happen all the time. The by now worn-out standard example is that of a stick partially immersed in water which seems to be crooked when looking at it, but which turns out to be straight when feeling it. (Note that we can only be sure that we are deceived visually here, if we assume that our sense of touch does not deceive us.)

The empiricist on 'er part can easily point at the many apriorist beliefs which have once been presented as 'indubitable truths', but which are now controversial or acknowledged to be false. Thus for apriorists it was once self-evident that one, and only one, line could be drawn parallel to another line thru a given point, that --what has later been denied by mathematicians believing in the existence of infinite sets-- a whole is greater than any of its parts, that in all change of the material world the quantity of matter remains unchanged (not 'of matter and/or energy'), and so on and so forth. (One idealist who tried to synthesize rationalism and empiricism said that the laws of science are not drawn from nature, but prescribed to it.)

The most egregious historical example of 'skeptical rationalism' is that of a philosopher who purported to doubt everything, but who, all the same, maintained that 'e had a 'clear and distinct' conception of one 'supremely perfect god'. It is in such monotheist dogmatism that 'skeptical rationalism' and 'empiricism' even used to meet each other, for also empiricists once claimed to have 'demonstrative knowledge of God's existence'. Altho their 'knowledge' was not apriori but empirical, the ideological result was the same, and had to be the same to start with. (It would of course have been equally dogmatical to claim that apriori intuition or empirical evidence would prove that there is not any god or demon.) One would expect that the end of this theist dogmatism was in sight when, with the synthesis of rationalism and empiricism, it was argued that the supernatural entities to which concepts like god, demon and immortality refer were beyond all possible experience, and could therefore never be objects of knowledge. What does the trick in this case tho, is a marked contrast between knowledge and faith, and the possibility not only of justified knowledge but also of justified faith which is not knowledge. (Faith in immortality but somehow not in preexistence, for instance.)

When hearing or reading the word faith one should bear in mind that this word is used in several senses. Three forms of faith which have been distinguished are: faith in spite of evidence to the contrary, in the absence of such evidence, and on account of evidence. Now, when contrasted with knowledge, faith means ungrounded belief so far as evidence is concerned, that is, faith in the absence of (and possibly in spite of) evidence to the contrary. But why would we have to have faith that there is at least one god, and that 'man' is immortal? According to one monotheist philosopher and ideologue, because 'man's nature demands it', because 'man is not merely an animal that knows but one that acts and feels'. One must have faith in this sort of reasoning to consider it as reasoning in the first place.

Another philosopher of later times has also admitted that there is no scientific evidence for or against the existence of gods or immortality, yet the justification of the belief in one or more gods, and the belief in immortality, is according to 'im that such beliefs are 'the deepest cravings of man'. Without them people's moral standards would collapse. On the pragmatist outlook of this philosopher --or should we say "ideologue" again?-- there is said to be a close connection between what is good and what is true. However, the close connection is not really between what is true and what is good, but rather between what is believed to be true and what is believed to be good by adherents of the same ideology, in this case of the same monotheist religion. If the right to believe something is indeed determined by the will to believe something in the absence of evidence, if not in spite of evidence to the contrary, then the right to disbelieve something is equally determined by the will to disbelieve something. The 'deepest craving' of some people may be a belief in gods, demons and immortality, yet the 'deepest craving' of other people is a belief in a conceptual austerity which does not allow for notions like god, demon (or names like God or Devil) and immortality. And while one group of people may defend the existence of one or more gods and immortality on the basis of their system of norms and values, other persons may reject the belief in the normative supremeness of such a god, or such gods, and/or in immortality on the basis of a different system of norms and values. (The very fact that they reject something on principle presupposes and requires moral standards.) Thus the pragmatist theory of truth is an instrument which merely 'justifies' opportunism.

The idealist distinction between knowledge and faith is itself not justifiable, for given that knowledge is grounded belief and given that it need not always be based on empirical evidence (altho it may never be contrary to it), there is no place for faith in the religious, that is, supernaturalist, sense. It is precisely religious faith and religious authority which have always been the pillars of denominational dogmatism. And it is in turn this religious dogmatism which has historically been most inimical to the advance of scientific knowledge, at least until its role was taken over by other forms of ideological dogmatism in politically totalitarian countries. If one can just take anything for gospel and present it as absolute, indubitable or infallible 'truth', this has nothing to do with knowledge or justification anymore. To call one's belief in such gospel 'truth' "religious science" or "(mono)theist science" or something similar with "-ology" --as has been done-- is, then, the ultimate corruption of language and a travesty of truth itself.