Humans have two kinds of beliefs, intuitive beliefs and reflective bel
iefs. Intuitive beliefs are a fundamental category of cognition, defin
ed in the architecture of the mind. They are formulated in an intuitiv
e mental lexicon. Humans are also capable of entertaining an indefinit
e variety of higher-order or 'reflective' propositional attitudes, man
y of which are of a credal sort. Reasons to hold reflective beliefs ar
e provided by other beliefs that describe the source of the reflective
belief as reliable, or that provide an explicit argument in favour of
the reflective belief. The mental lexicon of reflective beliefs inclu
des not only intuitive, but also reflective concepts.