"Reason is the servant of passions, as Hume said.
But passions need Reason: the magician’s customers are motivated by the passion
to survive, to see their crops grow; but nobody would consider that this passion in
itself is an adequate explanation for their magical beliefs.

The theory of rationality that I have sketched raises some important questions
that I will content myself with mentioning. Does the fact that behavior and beliefs
are normally inspired by strong reasons, even though these reasons might be false,
mean that any behavior or belief can be justified? Certainly not. Priestley believed
in phlogiston; Lavoisier did not. The two had strong reasons for believing what
they believed, and they both saw their reasons as valid. The latter was right, the
former wrong, however. The strength of reasons is thus a function of the context.
Today, our cognitive context is such that Priestley’s reasons are now weak for us
because we know that Lavoisier’s reasons were stronger. But Lavoisier’s reasons
had to be thought up and publicized before there could be any conclusion that he
was right. Then he became irreversibly right as opposed to Priestley. No relativism
follows from the contextuality of reasons.