demands on the sources

In the analysis above, there are six qualities that are presupposed in the notion of truth. Thus, we may prefer or even demand that our sources have these qualities.

necessity

We saw that Rationalism is necessary. None of the other sources are necessary.

usefulness

It is my impression that in accepting or rejecting a source of truth, people find utilitarian arguments to be the most compelling.

Empiricism is a very useful source. Especially if one has to negotiate traffic or open a can of soup. In those cases, even the most ardent non-realist happily relies on Empiricism.

In medieval Europe, the Church was unchallenged in wealth, power and respect. Perhaps as a consequence, Catholic doctrine was unchallenged. That changed when a new class of wealthy and powerful merchants arose.

Nowadays, the victories of science are many: a man on the moon, a cure for most diseases, a TV in your home. This appears to be a convincing argument for the scientific sources: Empiricism and Rationalism. It has also discredited the religious sources of Fundamentalism and Authoritarianism.

On the other hand, there is a utilitarian argument for Fundamentalism that still holds its ground. Fundamentalism provides us with a moral compass. I find attempts to derive morality from Rationalism and Empiricism not convincing.

There are other utilitarian arguments for the closely associated doctrines of Fundamentalism and Authoritarianism.

Fundamentalism provides 'learned men' with power over illiterates. Authoritarianism provides figures of authority with power over the masses.

Finally, Coincidentialism and/or Subjectivism are employed by charlatans, when these sources are conducive to obtaining wealth or attention.

consistency

Both Subjectivism and Authoritarianism are open to inconsistency. Fundamentalism is suspect. Some inconsistencies in the Bible are discussed in appendix B. Other holy scriptures probably fare no better.

An interesting case is Empiricism. It is the one source that has never shown inconsistencies, at least not that I am aware of. A red apple does not arbitrarily change its color to green. The case for rationality is complicated. It is obvious that human reason can be inconsistent on an individual level. To err is only human. It is quite another matter whether human reason is theoretically capable of full consistency.

Consider Russell's paradox. It appeared to Russell without warning, after all other mathematicians had overlooked it. A similar thing happened in cosmology, with Olbers' paradox. And a compelling example of inconsistent human reason may come from quantum-mechanics: Schrödinger's paradox (see appendix C).

These paradoxes suggest that we can never trust human reason to be fully consistent, and possibly that we need to make our peace with its inconsistency.

objectivity

Two sources appear to qualify as objective: Fundamentalism and Empiricism. Fundamentalism is objective since a scripture contains the identical text for every reader. Empiricism qualifies as objective as well. Of course, there are examples where matters appear differently to different people, but I am not aware of any example where these differing perceptions of the external world persist when all circumstances have been made to match. Or is it that those who persist in a different perception are considered to be delusional?

In fact, the objectivity and the consistency of Empiricism are important foundations for science, since they provide for the repeatability of experiments.

Subjectivism is the subjective source par excellence. In fact, it is so subjective that it ought to be the end of any debate. Arguing with a subjectivist invariably ends in frustration, usually for both sides.

It is not so easy to qualify Rationalism as either objective or subjective. It seems subjective in that intuition is a personal and private matter. On the other hand, no-one has formulated a competing Pythagorean Theorem; mathematical intuitions seem identical for every-one.

univocality

Again, two sources appear, prima facie, to qualify as univocal: Fundamentalism and Empiricism. But in the case of Fundamentalism, this first impression proves deceptive. See also chapter 4.

In fact, all sources that are expressed in natural language (Fundamentalism, Authoritarianism and Subjectivism) may qualify as equivocal. It is also doubtful whether Rationalism is univocal. Again, to err is only human.

nominality

A fair share of human discourse is nominal. As with equivocality, all sources that are expressed in natural language are open to nominality.