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Criticism 1: The Decomposition is Arbitrary

The Popper-Miller theorem works by splitting any prediction h into two pieces and then showing the evidence always hurts one of them. The entire argument rises or falls on whether that split is the right one. This is the most common objection in the literature.

Say your prediction is "it will rain tomorrow" and your evidence is "the barometer is falling." They split the prediction into:

• "Rain OR barometer falling": the part that overlaps with the evidence
• "Rain OR barometer NOT falling": the part that "goes beyond" the evidence

The evidence trivially supports the first part. But it hurts the second: you now know the barometer IS falling, which kills the "barometer not falling" escape route, so the whole thing narrows to just "rain", a harder path than before. Popper and Miller call this second part the "inductive content," show it always gets negative support, and declare induction impossible.

But this is not the only way to carve up "it will rain." You could split it into

• "rain AND barometer falling" OR
• "rain AND barometer NOT falling"

And now the evidence clearly boosts the first piece. Or you could not split it at all and just ask: does a falling barometer raise the probability of rain? Yes. That's inductive support, no decomposition needed. Only Popper and Miller's particular carving guarantees the "beyond" part always gets hurt.

So why this split? Their rule: the part that "goes beyond" the evidence must share no nontrivial logical consequences with it. The "beyond" part and the evidence must have absolutely nothing in common*. The only proposition satisfying this is (h ∨ ¬e), which forces the decomposition and makes the theorem work.

Philosopher Charles Chihara argued this rule is way too strict. Consider:

• Prediction: "All metals expand when heated"
• Evidence: "This rod is copper"

Together these yield: "This copper rod will expand when heated." Neither alone tells you that. It clearly goes beyond the evidence. But under Popper and Miller's rule it doesn't count, because it shares a consequence with the evidence (both mention this copper rod). Chihara's alternative: k "goes beyond" e if e does not logically entail k.

Under this looser definition, the negative support result disappears. He published this with Donald Gillies, who had earlier defended the theorem but agreed the decomposition question needed revisiting. (Chihara & Gillies, 1990, PDF)

Ellery Eells made a related point: look at "rain OR barometer NOT falling": it welds your weather prediction to the negation of your barometric reading. That's not a clean extraction of "the part about rain that has nothing to do with barometers." It's a Frankenstein proposition the algebra created. Eells argued this assumption has been "almost uniformly rejected" in the literature. (Eells, 1988, PDF)

#4322·Dirk MeulenbeltOP revised 1 day ago