4. Conscience is not infallible: it may err, like any other human judgment. A man may be blind, if not exactly to his own action, at least to the motives and circumstances of his action. He may have got hold of a wrong general principle of conduct. He may be in error as to the application of his principle to the actual facts. In all these ways, what we may call the _conscientious syllogism_ may be at fault, like any other syllogism. It may be a bad syllogism, either in logical form, or in the matter of fact asserted in the premisses. This is an _erroneous conscience_. But, for action contemplated, even an erroneous conscience is an authoritative decision. If it points to an obligation, however mistakenly, we are bound either to act upon the judgment or get it reversed. We must not contradict our own reason: such contradiction is moral evil, (c. v., s. iii., n. 3, p. 74.) If conscience by mistake sets us free of what is objectively our bounden duty, we are not there and then bound to that duty: but we may be bound at once to get that verdict of conscience overhauled and reconsidered. Conscience in this case has proceeded in ignorance, which ignorance will be either _vincible_ or _invincible_, and must be treated according to the rules provided in the matter of _ignorance_, (c. iii., s. i., nn. 3-5, p. 27). An obligation, neglected in invincible ignorance, makes a merely _material sin_. (c. iii., s. ii., n. 7, p. 33.) 5. There is another element of mind, often confounded under one name with conscience, but distinct from it, as a habit from an act, and as principles from their application. This element the schoolmen called _synderesis_. [Footnote 10] [Footnote 10: On the derivation of this word, whether from [Greek: synedaesis] or [Greek: syntaeresis], see _Athenæum_, 1877, vol. i., pp. 738, 798, vol. iii. pp. 16, 48.]