 The qualitative notions of confirmation as firmness and as relevance are demonstrably distinct. Unlike firmness, relevance confirmation can not be formalized by the final probability alone, or any increasing function thereof. To illustrate, the probability of an otherwise very rare disease \((h)\) can be quite low even after a relevant positive test result \((e)\); yet \(h\) is relevance-confirmed by \(e\) to the extent that its probability rises thereby. By the same token, the probability of the absence of the disease \((\neg h)\) can be quite high despite the positive test result \((e)\), yet \(\neg h\) is relevance-disconfirmed by \(e\) to the extent that its probability decreases thereby. Perhaps surprisingly, the distinction between firmness and relevance confirmation—“extremely fundamental” and yet “sometimes unnoticed”, as Salmon (1969, 48–49) put it—had to be stressed time and again to achieve theoretical clarity in philosophy (e.g., Popper 1954; Peijnenburg 2012) as well as in other domains concerned, such as artificial intelligence and the psychology of reasoning (see Horvitz and Heckerman 1986; Crupi, Fitelson, and Tentori 2008; Shogenji 2012).