Summa summae S. Thomae, Tomus II

Note 1°. Doubt is distinguished threefold: speculative, speculative-practical and practically-practical. Merely speculative is that which turns upon the nature, substance, value, quality and condition of things, whether speculative or moral: as if you doubt whether the angelic nature is universal, whether baptism conferred in rose water is valid. Speculative-practical is that which turns upon the goodness or malice, licitness or illicitness of an act in itself and in common, which goodness or malice is called objective and material: as if you doubt whether it is licit to baptize in rose water, to journey on a feast day, etc. Practically-practical is that which turns upon the goodness or malice, licitness or illicitness of an act to be done here and now, with all the circumstances attended to, which is called formal goodness or malice: as if you doubt whether it is licit for you here and now to baptize in rose water a dying infant.

What I said of doubt must be said of judgment, namely that it is threefold: merely speculative, concerning the nature or quality of things; speculative-practical, concerning the objective goodness or malice of actions; and practically-practical, concerning the formal goodness or malice of actions.

That the doubt or judgment which we call speculative-practical may be such, it must regard action in itself indeed, but as to be exercised, or in order to practice, and to influence it, inasmuch as from it the doubt or judgment practically-practical is formed: otherwise it will be purely speculative. But in the doubt or judgment alone practically-practical is situated the doubtful or probable conscience.

Note 2° doubt is again distinguished into negative and positive. Negative is, when there are no reasons or only very light ones for or against; and, as I already noted, it is improperly called doubt, and better named nescience or ignorance. Whence they err who recognize this doubt alone as doubt properly so called. Positive doubt is, when because of contrary reasons, on either side equally or nearly equally probable, the mind fluctuates suspended between both parts, assenting to neither.

Note 3°. Certitude, which is opposed to doubt, can be distinguished threefold: metaphysical, physical and moral. Metaphysical certitude is the adherence of the mind to truth which cannot be otherwise even by God, as: The whole is greater than its part; anything either is or is not. Physical certitude is the assent to truth which cannot be otherwise according to ordinary laws, although it could be otherwise through miracle, as a faggot thrown into fire to burn. Moral certitude is the assent to some truth founded and reasonable without fear of the opposite, although the opposite could absolutely and without miracle be, such as is that which is had in law through two witnesses worthy of faith, or that which is had about the baptism of anyone from the baptismal register; because, although it could happen that two witnesses held worthy of faith depose falsely, and that the pastor wrote falsely, yet that rarely happens, and it is a remote danger, which ought not prudently to be feared: otherwise there would be no end of doubts. These observations run through various parts of Theology; whence, set down once for all, they are to be firmly retained in memory.

I say: It is never licit to act with a doubtful conscience, probable or more probable properly so called ¹]

instead of a probable or more probable practically-practical doubt or judgment concerning the formal goodness or malice of the action; but only a morally certain conscience is the rule of our actions. It is certain and common, even among probabilists.

It is proved. 1° Conscience is the immediate rule of our actions. But a rule ought to be certain and infallible, at least morally: otherwise it would not be proposed as a rule, but would be regulable. Therefore.

2° He who acts with a doubtful conscience, probable or only more probable, does not act prudently. Therefore he sins. — The antecedent is proved. That anyone may act prudently, he ought to have no reasonable and founded fear of the formal dishonesty of his act; for the act of prudence is always practically true and morally certain. But he who acts with a doubtful conscience, or one only probable and more probable, concerning the formal honesty of his act, has a reasonable and founded fear of the formal dishonesty of his act, because those consciences do not go beyond the bounds of probability or opinion, whose account it is that it is with reasonable and founded fear of the opposite; and otherwise, if there were not reasonable and founded fear, it would already be moral certitude. — It is confirmed. He who takes a drink of which he doubts whether it is poisoned, or which he believes only probably and more probably not to be poisoned, while he has another not poisoned, acts imprudently. Therefore similarly.

3° He who does what he reasonably suspects offends God, by this very fact offends him, and contemns his friendship; just as he who would do what he reasonably suspects offends a friend, by this very fact would offend him and contemn his friendship. But he who acts with a doubtful conscience, probable or only more probable, does what he reasonably suspects offends God. Therefore.

[Perplexed, that is, when someone, placed between two precepts, one of which cannot be fulfilled without the other being omitted, remains in doubt which of the two he ought to prefer, and believes he will sin by omitting either one.

I answer. 1ª If the perplexed person can suspend the action, he is bound to defer it until he has consulted his confessor or another man expert and prudent, by whose judgment his conscience be formed.

2° If he cannot consult and there is present necessity of acting, because the action cannot be suspended without grave damage, then he is bound to choose the lesser evil, avoiding rather the transgression of the natural law than of the divine or human positive law; for the law of the lower order must always yield to the law of the higher order. It is supposed however that, in departing from the precept of lesser weight, he does not intend evil, but rather so acts as to avoid evil.

3° If both precepts seem equally grave to him, or he does not discern what the lesser evil is, let him choose whichever part, he will not sin, because in this case the liberty required for sinning formally is lacking, and from elsewhere necessity of sinning is never given. — So St. Alph., lib. I, tract. 1, n. 10, and Gury, n. 43.]

We resolved in the preceding dissertation, from the common opinion, that it is not licit to act with a doubtful conscience, probable or more probable, but that only a morally certain conscience is the rule of our actions. Now we ask whether upon an opinion or speculative-practical judgment, probable or more probable, concerning the objective and material honesty of an action, there can be founded mediately, namely through reflex principles intervening, a morally certain conscience concerning the formal and subjective honesty of the action; consequently whether it is licit