footnote 3). Given a query regarding the truth value of $F$, a reasoner may not only return ’true’ or ’false’, but also attach the value of $E(S, F)$ to the answer to give a measure of credibility of the latter. In cases where accepting an erroneous answer can have very undesirable consequences, a query can require a certain level of credibility, for example, ignoring answers with evidence less than 0.9.

Oblivious vs. non-oblivious reasoning
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In the absence of sufficient statistical information the evidence $E(S, F)$ is regarded as an approximation of the probability $p(F)$ that $F$ is true in a randomly chosen possible world, that is the probability that the belief in the truth of $F$ is correct in the present state of $W$.

Consider a reasoner $R$ that forms beliefs in order to answer a series of queries $F_1, \ldots , F_k$. Denote by $R(F_i)$ his belief regarding the truth of $F_i$. If the reasoner computes $R(F_i)$ as his answer to $F_i$ without taking into account the previous beliefs $R(F_j)$ ($1 \le j < i$) preceding $R(F_i)$, let us call this way of reasoning *oblivious*. Then if it turns out that there is no model of $S$ in 