(Repeating some of “Policy debates should not appear one-sided”, but expanding upon it and then countering “Multiple Factor Explanations Should Not Appear One-Sided”.)

If asked directly, most people who consider themselves sophisticated thinkers would probably agree that “acknowledging trade-offs” regarding your proposed policy is the right thing to do. In other words, they would agree that policy debates should not appear one-sided. But if you only ever hear that side of the message, you might apply it to questions of facts as well, where it is not the correct stance. So, let us first investigate why questions of fact should actually appear one-sided.

The evidence for facts is one-sided

Consider the question of whether Earthly life arose by natural selection. If this were true, then it would have had a profound impact on everything in our world. That is, the answer to the question of whether or not the theory of natural selection is true, strongly affects the answer to other questions we can ask about the world. The following graphical model is meant to visualize this. The arrows indicate the direction of causality: if Earthly life arose by natural selection, then this is the cause (or one cause) for our finding fossils of extinct animals. It is not the fact that fossils came first and somehow caused natural selection.

causal diagram 1

(Evo: “Earthly life arose by natural selection”, Fos: “there are fossils from extinct species”, DNA: “the genetic code of all life on Earth is encoded by DNA”, Nic: “species occupy their own peculiar ecological niche”, Emb: “embryos from different species look very similar”, Psy: “human psychology is adapted to the living environment during the pleistocene”)

Now, suppose you have heard of this theory but you haven't seen any evidence yet. (A highly unusual situation for a scientist – the hard part always is coming up with the hypothesis, and not finding the evidence.) So, you have the theory and the graph it induces, but you don’t yet know whether the graph actually corresponds to reality; you cannot tell with your current state of knowledge. One day, you find fossils. This increases the credence you give to this theory but it's not certain yet; there may yet be other plausible theories. Next, you observe Darwin's finches on the Galápagos Islands and it strikes you how well they are adapted to different food sources. Evo goes up in probability a...

Affect Heuristic

See also