PERTINACITY. - Insofar as it is constancy in any operation, or insofar as it is manifested in one who does not allow himself to be moved by difficulties, it is nothing perseverance (v.) exercised in an eminent manner; but in the specific sense, that of stubbornness and obstinacy, it is conceived as a vice opposed to perseverance by excess, that is, according to s. Tommaso, Sum. Theol., 2ª-2ª, q. 138, a. 2, as “persevering in one’s own opinion more than is fitting.”
This occurs through unwillingness to assent to another’s opinion, even if better, in order not to appear less wise. P. is also persistence in doing evil, whereas perseverance is constancy in doing good. Generally p. arises from pride, whereas inconstancy derives from frivolity, a vice opposed to perseverance by defect.
P. in denying one or more truths revealed by God and proposed by the Church for belief enters as an essential element into heresy (v.).