A Case of Conscience is a science fiction novel by American writer James Blish, first published in 1958.

It is the story of a Jesuit who investigates an alien race that has no religion yet has a perfect, innate sense of morality, a situation which conflicts with Catholic teaching.

In 2049, Father Ramon Ruiz-Sanchez of Peru, Clerk Regular of the Society of Jesus, is a member of a four-man team of scientists sent to the planet Lithia to determine if it can be opened to human contact.

While on a walking survey of the land, Cleaver, a physicist, is poisoned by a plant, despite a protective suit, and he suffers badly.

The information Chtexa revealed to him, added to what he already knew, convinces him that Lithia is nothing less than the work of Satan, a place deliberately constructed to show peace, logic, and understanding in the complete absence of God.

Michelis is mystified, but does point out that all the Lithian science he has learned, while perfectly logical, rests on highly questionable assumptions.

At this point, the Jesuit solves a riddle which he has been pondering for some time, from Book III of Finnegans Wake by James Joyce (pp.

572–3), which proposes a complex case of marital morals, ending with the question "Has he hegemony and shall she submit?"

Pope Hadrian VIII, a logically and technologically aware Norwegian, points out two things Ruiz-Sanchez missed.

The priest bows his head in shame that he has overlooked an obvious solution to his own case of conscience while he was absorbed in "a book [Finnegans Wake] which to all intents and purposes might have been dictated by the Adversary himself ... 628 pages of compulsive demoniac chatter."

A violent mass riot breaks out, fomented by Egtverchi and made possible by the psychosis present in many of the citizens as a result of living in the 'shelter state' (an earlier reference to the "Corridor Riots of 1993" indicates that this is not the first time violence has burst out among the buried cities).

Michelis and Ruiz-Sanchez are taken to the Moon, where a new telescope has been assembled, based on "a fundamental twist on the Haertel equations which makes it possible to see around normal space-time, as well as travel around it"[1] so that the instrument presents a view of Lithia in real time, bypassing the delay caused by the speed of light.

The planet explodes, eliminating Cleaver and Egtverchi, but also Chtexa and all the things Ruiz-Sanchez admired.

While faulting the novel for "extreme unevenness", Galaxy reviewer Floyd C. Gale concluded that A Case of Conscience was "a provocative, serious, commendable work" and characterized it as "trailblaz[ing]".

He also received, and quoted, the official Church policy on contact with extraterrestrial intelligent life forms.