How can I know anything?

This is the reply to the skeptic, who has argued persistently (if not always convincingly) from the very beginning that, when you really think about it, there’s no proof that we know anything. And I don’t mean that 2 + 2 = 4 and the like. I mean ANYTHING — that you exist, that the universe is, that you aren’t a brain in a vat (or a computer simulation of a brain in a vat) living a complex virtual reality, and so on.

The standard philosophical definition of knowledge is “true, justified belief.” That is, we know something if it’s true and if we believe it because we have good reason to believe it (versus believing it for bad reasons, or just on accident). The problem with that definition, the skeptic warns, is that there doesn’t seem to be a universally applicable benchmark of truth. What independent source can verify that our true, justified beliefs are in fact true? Even if some advanced alien race came down from the heavens to impart universal wisdom, how would we know that it wasn’t all just as much as sham as any of the rest of it?

We wouldn’t, says the skeptic. And science is no help since what it produces is not truth but provisional knowledge forever subject to cancellation or revision by future discovery. In fact, what makes something scientific is its falsifiability — no matter how improbable, as long as it is possible a theory could be overturned, then it is not absolute truth. What’s more, no internally consistent scientific account of the universe would be able to tell the difference between reality and a sufficiently advanced simulation of the same.

Hence almost everyone tends to ignore the question of absolute truth and instead focuses on the question of justification. If we can’t prove beyond all doubt that we know anything, what at least counts as sufficient reason to accept a proposition? Where should we set the bar?

Here people tend to fall into one of two camps: empiricists and rationalists. The latter argue that the first seeds of knowledge, the foundation from which we can deduce all the rest of it, is either innate — say, provided by God or Nature as a fundamental quality of the universe, like the Planck length — or else derivable from logically necessary first principles, which is what Descartes was trying to do with his famous Cogito ergo sum — I think, therefore I am.

Hogwash, say the empiricists. Deducing the nature of the deep universe from the comfort of your armchair is about as effective as quarterbacking from the same. Knowledge can only come from engagement with the world, from experience. We know only what we can go out into the world and demonstrate through observation and testing. Anything else is intellectual masturbation.

To understand just how fascinating this debate can be, take the famous ontological argument of St. Anselm (circa 11th Century). Says Anselm, God is a being than which none greater can be conceived, therefore He must exist, because if He did not, we would have a paradox: a greater being could yet be conceived — namely, one that had all the same superlative qualities but with the additional quality of existence. Therefore, a being than which none greater can be conceived must logically exist. Therefore, God exists.

The logical cleanliness of such reasoning appeals to a rationalist, whereas an empiricist would argue, no matter how clean it appears, nowhere is it demonstrated than any such thing actually is, let alone that it’s all-good or all-knowing or even the Christian (versus some other) God. The empiricist stands on the threshold of the world and asks, Where’s the Beef?

What makes this such a fascinating example, however, is not the arguments themselves but the importance of cultural context. These days, at least in the West, we’re all enamored of science, even the faithful (which is something of an oxymoron), but in the 18th and 19th centuries, rationalism was nearly synonymous with atheism. Before Darwin and inflationary cosmology, the primary evidence for God, who was the basis of all knowledge, was assumed to be practical, empirical, and only those silly atheists went about trying to deduce everything with wit and reason. If you wanted to see whether or not God made the world, went the argument, just look around you.

But the act of looking, as Kant showed, comes fully loaded with cultural preconceptions. Contemporary philosophers of science call this the “theory laden-ness” of facts, that raw data often tends to be filtered through the commonly accepted theoretical explanation. The world is complex, after all, so complex that it’s easy for all of us to see what we want to see, and to find evidence for it, which is what makes this question so important.

But regardless of your preference, the simple fact is, none of us are purely rationalist or purely empiricist in daily life, not even the scientist, who both demonstrates AND deduces. In the ongoing quest for a benchmark of knowledge, there is a place for both. Unfortunately, neither yet has a good response to the skeptic.