P1) If experimental evidence is required for a sound causal inference and confounding is a causal concept, then experimental evidence is required to validate potential confounders.
(P∧Q→R)
P2) Experimental evidence is required for a sound causal inference.
(P)
P3) Confounding is a causal concept.
(Q)
C) Therefore, experimental evidence is required to validate potential confounders.
(∴R)