That child is drowning. You should help her.
When you’re not wearing your philosophy pants, you might find the second sentence of this coolly-stated argument to flow naturally from the first. But when you’re forced to abide by the laws of logic, you may suddenly find the procession from the one to the other impossible. The difficulty is that the first sentence expresses a descriptive fact about the way the world is, while the second expresses a value, a prescription of what one ought to do, that appears to make no necessary reference to the fact.
The conceptual gap between these two kinds of statements is made explicit by the brilliant 18th century Scottish philosopher David Hume. In the Treatise of Human Nature, Hume observes that philosophers ‘proceed for some time in the ordinary way of reasoning’ with regard to observations concerning human affairs, ‘when of a sudden, I am surprised to find that instead of the usual copulations of is and is not, I meet with no proposition that is not connected with an ought, or an ought not. As this ought or ought not expresses some new relation or affirmation ‘tis necessary that it be observed and explained; and at the same time a reason should be given for what seems altogether inconceivable, how this new relation can be a deduction from others which are entirely different from it’ (Bk 1, Pt 1, §1).
I don’t wish to disagree with Hume that values are not logically entailed by facts about the world, and that the two are conceptually distinct. And this is, as far as I understand, all that he meant to uphold. But there is a more radical construal of the fact/value dichotomy, sometimes left unarticulated but pervasive in popular thought, according to which fact and value come apart in reality; the two are not only conceptually but are fundamentally distinct. I think this misunderstanding arises from and is reinforced by the abstract cases that make it difficult to see that facts come packaged with values.
It is true that in the case of deductive reasoning, which makes use of propositions abstracted from concrete states of affairs, facts and values are employed in a way that makes them seem wholly independent from one another. But it seems this way not because facts are in reality devoid of value. What is easily overlooked is that somebody selected that fact, among infinitely many others, as worthy of attending to. When the descriptive fact, “that child is drowning”, is declared by a concerned onlooker, it is selected among so many possible alternative facts (e.g. “the water is warm” and “that is a nice bathing suit”). It is chosen because the concerned onlooker considers it more worthy than these other relatively unimportant facts. And when I choose to use “That child is drowning” as an example of a descriptive fact, I am selecting it in favor of other possible examples because I consider it a better way to illustrate the concept of a descriptive fact. That is the value from which the fact is borne out.
The motives that guide a selection among facts, though they’re sometimes suggested by the context, are seldom suggested by the bare fact. They can be especially well hidden when the facts are at a second or third remove from a concrete state of affairs, like in the case of scientific claims or the premises of an argument. But that the presence of value in fact is disguised or dimly perceived is an epistemological difficulty, and to conclude from that difficulty that facts and values are two fundamentally different species, completely independent and never interacting, is a mistake. In reality, facts and values are co-instantiated, and to separate them is to rip reality in two.