Propositional knowledge is “knowledge that ...”. It is opposed to “knowledge how”.
p is true (corresponds to how things are).
I can give reasons (justify) my belief that p.
Plato’s dialog Theatetus – which you are welcome to read – explains this view in detail.
Knowledge, then, is justified true belief.
Some people (e.g., the philosopher Descartes) say we can’t know p unless we’re absolutely certain that p.
Does knowledge require absolute certainty? No. We all believe things we’re not absolutely certain of (e.g., that the sun will rise tomorrow, that we have bodies, etc.). But we have very good reasons to believe the sun will rise tomorrow and that we have bodies. Those reasons are sufficient to say we know the sun will rise tomorrow, for all practical purposes. If we ever encounter good reasons to doubt that the sun will rise tomorrow (say we discover that earth might be knocked out of orbit in the near future by an asteroid), then we can say we don’t know. But as long as we have no good reasons to doubt that the sun will rise tomorrow, we can say we know it. We can say we know p if we have good reasons for believing p.
Radical philosophical skepticism (the view that we can’t really know anything) is unreasonable (because we do seem to know some things), self-contradictory (because the skeptic claims to know that he cannot know), and vacuous (because we cannot help but behave as though we know some things).
So the next interesting question is: what are good reasons? What makes p a justified belief?
What counts as justified belief?
Belief that p is not justified if we have good reason to doubt p.
Thus (by contraposition) belief that p is justified if we have no good reason to doubt p.
We also say belief that p is justified if p is the best explanation for the observed phenomena.
Of course, skeptics are right that beliefs true beyond reasonable doubt might still be false.
But in most contexts, “true beyond reasonable doubt” is sufficient for claiming knowledge.
We should doubt if p conflicts with (is inconsistent with) the rest of our reasonable beliefs.
We should doubt if p conflicts with (is inconsistent with) our background information – our general world knowledge.
We should doubt if p conflicts with genuine expert opinion.
Coherence of p with our other beliefs is not sufficient to establish p.
Ideologies (for example, Marxism, Freudianism, Christianity) are completely coherent; everything fits together and every phenomenon can be explained. But the whole self-contained system might be wrong, since these systems are consistent with all states of affairs.
But remember Chapter 3: other things are not always equal.
Is faith ever a source of knowledge?
Faith is precisely unjustified belief. If knowledge is justified belief, faith cannot be a source of knowledge.
James’ precursive faith: e.g., believing that someone likes you (in order to bring it about), or the stranded mountain climber example.
Is “intuition” ever a source of knowledge?
What do we mean by “intuition”? ESP? HSP?
There is no good reason to believe in extra-sensory perception (ESP).
But what about hyper-sensory perception (HSP), as “evidenced” by Sherlock Holmes, Counselor Troi, Clever Hans, Ilga K (115)? Yes! HSP is well-established, e.g., by Rosenthal’s experiments (114). But it’s not ESP.
Is “mystical experience” ever a source of knowledge?
Capra and LeShan say mystical experience is a “privileged road” to knowledge.
Capra in his famous book The Tao of Physics argues that modern physics and Eastern mysticism, surprisingly, are in perfect agreement about the ultimate nature of reality. At the largest and smallest levels of being, all distinctions disappear, logic becomes useless, self and non-self merge, temporal distinctions melt away, and everything is connected to everything else (“everything is one”).
In mystical experience, you are supposed to gain a new understanding of the universe and your place in it. Typically, the mystic claims to experience ecstatic unity with a magnificent indescribable and benevolent reality.
Some mystics claim that the self merges with this reality and disappears; others claim the self persists, as in a sexual union. Buddhists claim there’s no self to begin with. There seems to be a variety of mystical experiences. Christian mystics experience union with Christian figures; Hindu mystics with Brahman, or lesser gods, etc.