Obviously the matter of interpretation gave abundant scope for
casuistry. Bernard Gui's 'Practica' is an illustration of this. There
was an obvious temptation for the inquisitor to discover heresy in all
manner of disguises.[365] Heresy was conceived as a most insidious as
well as a most pernicious enemy, to be ferreted out in all sorts of
strange lurking-places. The indefiniteness of the term--the inquisitor's
definition is always a catalogue--was as a matter of fact unavoidable,
seeing that the offence consisted, not in an overt act, but in an
intention. It was a crime of the intellect, a matter of the state of
a man's mind and disposition. Sometimes the heresy might be revealed
in an act, but very often there would be no formal act at all. The
inquisitor must be a searcher of the heart and a prober into the
obscure workings of the mind.[366] It is necessary to add one simpler
but important point. No one could be a heretic unless he had been
baptized, unless he was a member of the Christian Church.[367] The
infidel, the Turk, the Jew, did not come within the Inquisition's
purview--unless he had at one time received the Christian religion.
By birth or adoption the heretic must have been a Christian: for
the heinousness of his crime consists in its being a repudiation, a
rebellion.