third unbelief, he sins against prudence, if he has no good grounds for his opinion, or against the respect due the Church, if he is moved by contempt for its judgment. In a conversation between A, B, C, D and E, the following opinions are defended. A thinks that any use of natural knowledge with reference to matters of faith is wrong; B, that the theologian should employ mathematics and physical science, but avoid reasoning and philosophy; C, that the method and principles of Scholasticism are not suited to our ago or to all peoples; D, that the psychology and cosmology of the Scholastics should be remade entirely; E, that many hypotheses of Aristotle in physics have been proved false. The opinion of A contains heresies condemned in the Vatican Council regarding the preambles of faith and the motives of credibility. The opinions of B and C are at least contrary to the religious assent due the authority of the Church (see Denzinger, Enchiridion, nn. 1652, 1680, 1713, Code of Canon Law, Canon 1366, Sec.2, _Humani Generis_, n. 11-14). The opinion of D, as it stands, contains a denial of several doctrines of faith, such as the immortality of the soul and the creation of the world, and is thus implicitly heretical. The opinion of E is true and admitted by all. (c) By “opposed” to faith is meant any judgment which, according to the logical rules of opposition between propositions, is irreconcilable with the truth of a formula of dogma or of a censure of heresy. Examples: The Council of Trent defined that “all sins committed after Baptism can be forgiven in the Sacrament of Penance.” It would be heretical, therefore, to hold that “no sins committed after Baptism can be pardoned in the Sacrament of Penance” (contrary opposition), or that “some sins committed after Baptism cannot be absolved” (contradictory opposition), Similarly, the Council of Trent (Sess. VI, Can. 7) rejected the proposition that “all Works done before justification are sinful,” and hence according to Logic the contradictory--viz., that “some works before justification are not sinful”--is of faith, for two contradictories cannot both be false; the contrary--viz., that “no works before justification are sinful”--is not, however, defined, for two contraries can both be false. (d) Heresy is “manifestly opposed to faith.” He who denies what is only probably a matter of faith, is not guilty of heresy. Example: The Instruction of Eugenius IV on the matter of the Sacraments is held by some authorities of note not to be a definition, and hence those who accept opposite theories are not on that account heretical.