 As with analyticity, deducibility can obtain for all sorts of reasons, necessary or contingent, logical or non-logical, known or unknown. [Not all birds fly], for instance, is deducible from [Some birds don’t fly] with respect to [birds] and [fly], and [Buddy is a bird] is deducible from [Buddy is a crow] with respect to [Buddy], while [Harry Truman wasn’t a Buddhist] is also deducible from [Harry Truman was a 20th-century US president] with respect to [Harry Truman]. The last example shows that deducibility does not require that the connection between premises and conclusion be necessary, nor that it be knowable a priori (though, unsurprisingly, Bolzano held that there are cases of deducibility that are necessary, some of which are also knowable a priori). There is thus a clean isolation of truth-preservation as a phenomenon of intrinsic logical interest. 