Heresy, according to Karl Rahner, today is not so much a formulated, false religious doctrine as a hidden and latent phenomenon. Its peculiar danger is to remain implicit, not as in former times to be expressed in explicit propositions. It may indeed coexist with a verbal orthodoxy and an anxious, "correct" care never to express views that might conflict with the official doctrine. In the form of moral attitudes, moods and points of view, heresy today is not necessarily directed against the faith; it may even spring from Christian opposition to heresy or outmoded views. The author's object in tracing the changing pattern of heretical attitudes is not to encourage a hunt for secret heretics but to show that the means employed by the Church to combat heresy in the past, chiefly by official repression, are no longer effective. The battle against the modern form of implicit heresy is a task increasingly incumbent on the conscience of the individual. Where the teaching authority of the Church is no longer able, or only with great difficulty or in general terms, to denounce, the individual Christian is in a better position by prudent and wise vigilance to redress the false proportions, exaggerations and onesidedness of the faith.