[Absolute certainty about things we say that we "know"] is only attainable through revelation.I paraphrased the portion in brackets because there was some ambiguity in the source, which read more like, "To have knowledge is to know with absolute certainty."
Heh. That ("knowledge is knowing with certainty") reminds me of an old B.C. cartoon in which one of the characters opens Wiley's Dictionary and looks up the word "pollution." The definition: "The result of polluting." So he turns to the definition of "polluting" and reads there: "to pollute". So he turns to the definition of "pollute" and reads: "to cause pollution." At that point he sets fire to the dictionary, which belches forth a polluting smoke cloud. :-) Of course the point is that if a definition is self-referential, it's pretty hard to get out of the circle.
Maybe this is not an entirely fair way to characterize that definition of "knowledge," but it seems pretty hard to avoid. On the other hand, I suppose it's probably difficult to talk about "knowing" without becoming self-referential at times, so I'm not going to hold anyone's feet to the fire about that. Suffice it to say, though, that this is one source of my uncertainty about whether I've understood the author. :-) Maybe a better way of expressing the thought would be by way of contrast: it's not actual knowledge if you do not possess absolute certainty about it. Hence a property of knowledge is that the one who possesses it has absolute certainty about the subject of his knowledge.
[By the way, Aristotle characterized "knowledge" in pretty much the same way - namely, that one of its properties is that it is certain. He said that a lot of what people say they know really doesn't amount to much more than opinion. He didn't say that this knowledge came by way of revelation, though. But I digress.]
Our author says that "knowledge" defined like this can only be had "through revelation." There is a little fuzziness here, too. Does he mean that absolute certainty is available only "through" the Bible, or "through" direct revelation from God? Let's consider each possibility. If he means that we can obtain absolute certainty only through the Bible, then it seems to me that what he has said is unintelligible. If he really means that, then by the very nature of the case sensory perceptions are ruled out as a source of absolute certainty, and if that is so, then how will we get absolute certainty from the Bible? We must make use of our senses in some way in order to read or hear or touch (e.g., through Braille) Scripture; if we cannot have absolute certainty from what our senses tell us, then it is likewise impossible for us to have it about what we read or hear or touch in the Bible. The consequence of that, of course, is that absolute certainty would be absolutely impossible; hence the definition would leave us with no hope for any absolute certainty whatsoever.
If that's the case, then there really isn't a point in debating much of anything, is there? Everyone's opinion is as good as anyone else's, and those who claim otherwise would be blowing smoke in your eyes. Consequently it seems to me that this view is a real discussion-killer.
The second alternative is that he means we can only have absolute certainty by way of direct divine revelation. Now I certainly agree that this is a way of obtaining certainty, on a Christian understanding of things; but it should also be said that there are some silent assumptions about God here (and really, the same assumptions must be in force if we get certainty from the Bible, too): namely, that there is only one God, and that he is perfectly good and truthful (so that no evil god could tell us lies by means of direct revelation). Hopefully you see the obvious questions here:
Where do we get these ideas about God? How do we know (with absolute certainty) that God is trustworthy?
Hopefully it will be obvious that these are not idle questions for the man who insists that we can obtain certainty only through revelation (whether directly or through Scripture). He needs to have some reason to know that God is trustworthy, but on his own terms he has none, it seems to me.
Hopefully it will be equally obvious that I do not subscribe to this view of the question, although I suppose I probably held to something like it when I was a Protestant. I think that in fact we can have certainty about at least some things, and possibly even many things. A good example is the law of non-contradiction. A given thing 'A' cannot be 'X' and 'not-X' at the same time and in the same respect. We can know this with certainty. It is a logical impossibility. And speaking of logic, we can also know with absolute certainty the conclusion of a syllogism. If all men are mortal and Socrates is a man, then Socrates is mortal. Given the truth of the premises, the conclusion is likewise certain to be true.
This sort of knowledge doesn't come to us by way of revelation; it comes to us by way of reason. And so we can jump to the sed contra: We do not obtain absolute certainty solely by way of revelation, but also by means of reason. We can know, for example, that God is perfectly good (and consequently truthful); and because we can know this, we can trust his revelation to be absolutely truthful as well.
(that's a ridiculously brief summary of something that St. Thomas spends pages and pages discussing, both in the Summa Theologica and in the Summa Contra Gentiles)
This does not mean that reason is omnicompetent. We cannot deduce literally everything. But we can obtain certainty about many things by way of reason, and we would be foolish to suppose otherwise.
We can also obtain certainty by way of our senses. I know for certain that there is a keyboard in front of me, and that I am using it to type this sentence. Some folks are prone to say that our senses are not reliable, but I submit that these people do not spend much time fretting over whether the substance on their dinner plate is steak or grass clippings. If they were serious about their uncertainty, they certainly (!) would be worrying about that meal. :-) And how will they get that certainty out of the Bible if he can't trust his senses?