Consider a warrant (or its universal generalization) backed by a canonical testCanonical test taking account of all known relevant variablesRelevant variable. Suppose at each level of the test no relevant variableRelevant variable has a value constituting a counterexample to the warrant. There is thus no need to qualify the warrant with a ceteris paribus clause. The warrant is conclusive, here backed from below. Suppose that a warrant is backed by a universal generalization included in a system of taxonomy, for example the generalization that whales are mammals. The generalization is not qualified and the warrant is conclusive. But the warrant is still backed a posterioriBackinga posteriori. The system of taxonomy is based on observation, although the generalization is not accidental. The class of conclusive a posterioriBackinga posteriori warrants then is not empty.