Through a logical analysis, we show how Gettier cases, presented as counterexamples to the conception of knowledge as a justified true belief, are not consistent; they are a variation of oracular reasoning, logical fallacy in which specific type propositions, which contain a logical constant, are tangled with propositions formed by logical variables; uniqueness is confused with mere existence, the necessary and sufficient conditions with necessary but not sufficient conditions; and there are cognitive biases, for example, the neglect of base rates in argumentation.