Jesuits, then, were capable of the most extensive asset-stripping of ‘reason of state’. But the aspect of reason of state they found most difficult to sanitise was its attitude to fides, good faith. Ironically it was their stance on precisely this matter that earned them the most opprobrium. Machiavelli's maximally objectionable chapter 18 of his Prince was entitled ‘How princes should keep faith’ (Quomodo fides a principibus sit servanda). A near-synonym for fides was honestas. Among the standard accusations levelled at Jesuits was that they were themselves Machiavellians in defending lying and deceit (under the name of ‘equivocation’), and denying that ‘faith is to be kept with heretics’. A related charge was that Jesuits as a matter of policy insinuated themselves into the favour of all, but especially of princes, by the leniency of their casuistry.

In fact Jesuits taught no doctrine in these matters that was not also taught by other theologians, Protestant as well as Catholic. Their teaching was not monolithic and their casuistry was no more consistently lax than anyone else's. They were singled out for attack because of the fame of their casuists, because of their prominence in causes célèbres where fides and veracity were central issues, and they were made proxies for those whom their opponents (especially Catholics) did not dare to attack openly. The controverted issues in Jesuit casuistry related to what should count as breaches of the duties of fides and honestas.