Sometimes a hypothesis can be stated in such a way that a single counter-example will disprove it. The now classic example is that all swans are white. A single non-white swan will falsify this hypothesis. How thoroughly do you have to search, however, before we can conclude that all swans are white? Would you have to simultaneously survey every swan in the world? If it takes 10 years to conduct a thorough survey can you be sure that a black swan was not born in the last 10 years?
The problem here is in thinking in absolutes. Scientific theories, rather, often deal with probabilities and are not necessarily wrong when exceptions are found. In the case of swans, the more thoroughly we look for non-white swans without finding them the greater our confidence is that all swans are white, and we can certainly conclude that most swans are white and that any exceptions are rare.
While it is true that science does not deal with absolute conclusions, it doesn't follow that science doesn't involve absolutes at all. In fact, science can't be done without some thinking in absolutes. Consider those swans that are the subject of a worldwide survey. Assumed in the story is that scientists have no problem distinguishing swans from non-swans, be they black or white. We might say that, as far as the experiment is concerned, scientists are absolutely able to distinguish swans from non-swans.
Why, for instance, on encountering a creature that is furry, has floppy ears, and barks, doesn't a scientist announce a revolutionary discovery: Not only can swans be black, but they can have fur and floppy ears! Because, of course, what the scientist has encountered is a dog and not a swan. Experiments like the one described by Novella presuppose, albeit unconsciously, an Aristotelian natural philosophy - specifically, the distinction between essential and accidental properties of being. An essential property is a property that makes a being the kind of thing it is; an accidental property is a property that, whether a being has it or not, does not change the kind of thing it is.
How is it possible for us to make absolute statements regarding essential properties? How can we know, for instance, that while all swans may not be white, all swans are naturally born with the ability to fly? (I qualify that statement with "naturally" because, through accidents of birth or injury, a particular swan might not be able to fly. This does nothing to change the fact that its nature is directed toward flight and would have achieved it but for accidents of fate). Hume famously denied such a thing was possible with his criticism of induction. But what Hume overlooks is that when we analyze something, we not only understand it as a catalog of properties, but we also understand it's mode of being, the why behind its collection of properties. A swan has a mode of life peculiar to it, and very different from the mode of life of a dog, that accounts for the essential properties of the swan vs. a dog. A dog is an animal that hunts prey through smell, and so is built low to the ground with a wet nose and an extraordinary sense of smell. The swan eats plants at the bottom of ponds, and so has a long neck and a bill, but a poor sense of smell since it doesn't need it. The dog's nose is essential to its mode of being so we can be sure we will never encounter a dog with a bill, and similarly we won't find a swan with a soft wet nose. But being black or white is irrelevant to the mode of life of either, so we should expect that we might find different colored dogs or swans. And in that case, statistics tell us the probability of occurrence of the various colors.
If we don't like Aristotle, Kant saw the same thing with respect to the distinction between essential and accidental properties, but he hoped to avoid any metaphysical assertions concerning being. His solution was to relocate the essential/accidental distinction from being (i.e. in the world out there) to the subjective (i.e. in your mind). Kant argues that in order for experience to be possible for us at all, it must be organized by our cognitive faculties into some sort of coherence - otherwise our experience would be the "blooming, buzzing confusion" of William James. Actually, it would be worse than that, for Kant insists that it wouldn't be experience at all, not even a confused one ("confusion" still implies a relationship between the confused elements, some stable background with respect to which they are confused.) So the mind organizes experience spatially and temporally, with space and time being the terms in which the mind constructs that organization. Essence and accident are categories within which the mind refines experience. For Kant they are imposed on nature rather than read off it as with Aristotle. But it doesn't really matter for the purposes of this post, for they are just as absolute for Kant as they are for Aristotle; they are just subjectively absolute rather than objectively absolute. Either way, empirical investigation is impossible without some thinking in absolutes.