Watson's Biblical & Theological Dictionary 
the doctrine and science of conscience and its cases, with the rules and principles of resolving the same; drawn partly from natural reason, or equity, and partly from the authority of Scripture, the canon law, councils, fathers, &c. To casuistry belongs the decision of all difficulties arising about what a man may lawfully do or not do; what is sin or not sin; what things a man is obliged to do in order to discharge his duty, and what he may let alone without breach of it. Although the morality of the Gospel is distinguished by its purity and by its elevation, it is necessarily exhibited in a general form; certain leading principles are laid down; but the application of these to the innumerable cases which occur in the actual intercourse of life, is left to the understanding and the conscience of individuals. Had it been otherwise, the Christian code would have swelled to an extent which would have rendered it in a great degree useless; it would have been difficult or impossible to recollect all its provisions; and, minute as these would have been, they would still have been defective,— new situations or combinations of circumstances modifying duty continually arising, which it would have been impracticable or hurtful to anticipate. When the principles of duty are rightly unfolded, and when they are placed on a sound foundation, there is, to a fair mind, no difficulty in accommodating them to its own particular exigencies. A few cases, it is true, may occur, where it is a matter of doubt in what way men should act; but these are exceedingly rare, and the lives of vast numbers may come to an end without any of them happening to occasion perplexity. Every man may be, and perhaps is, sensible, that his errors are to be ascribed, not to his having been at a loss to know what he should have done, but to his deliberately or hastily violating what he saw to be right, or to his having allowed himself to confound, by vain and subtle distinctions, what, in the case of any one else, would have left in his mind no room for hesitation. The manner, however, in which the Gospel inculcates the law of God, combined with other causes in leading to a species of moral discussion, which, pretending to ascertain in every case what ought to be practised, and thus to afford plain and safe directions to the conscience, terminated in what has been denominated casuistry.
The schoolmen delighted in this species of intellectual labour. They transferred their zeal for the most fanciful and frivolous distinctions in what respected the doctrines of religion to its precepts; they anatomized the different virtues; nicely examined all the circumstances by which our estimate of them should be influenced; and they thus rendered the study of morality inextricable, confounded the natural notions of right and wrong, and so accustomed themselves and others to weigh their actions, that they could easily find some excuse for what was most culpable, while they continued under the impression that they were not deviating from what, as moral beings, was incumbent upon them. The corruption of manners which was introduced into the church during the dark ages rendered casuistry very popular; and, accordingly, many who affected to be the most enlightened writers of their age, and perhaps really were so, tortured their understanding or their fancy in solving cases of conscience, and often in polluting their own imaginations and those of others, by employing them on possible crimes, upon which, however unlikely was their occurrence in life, they were eager to pronounce a decision. The happy change which the Reformation produced upon the views of men respecting the sacred Scriptures, tended to erect that pure standard of duty which for ages had been laid in the dust. Yet for a considerable time Protestant divines occupied themselves with the intricacies of casuistry, thus in some degree shutting out the light which they had fortunately poured upon the world. The Lutheran theologians walked very much in the tract which the schoolmen had opened, although their decisions were much more consonant with Christianity; and it was not uncommon in some countries for ecclesiastical assemblies to devote part of their time to the resolution of questions which might have been safely left unnoticed, which now are almost universally regarded as frivolous, and about which almost the most ignorant would be ashamed to ask an opinion. Even after much of the sophistry, and much of the moral perversion connected with casuistry, were exploded, the form of that science was preserved, and many valuable moral principles in conformity to it delivered. The venerable Bishop Hall published a celebrated work, to which he gave the appellation of "Cases of Conscience Practically resolved;" and he introduces it with the following observations addressed to the reader: "Of all divinity, that part is most useful which determines cases of conscience; and of all cases of conscience, the practical are most necessary, as action is of more concernment than speculation; and of all practical cases, those which are of most common use are of so much greater necessity and benefit to be resolved, as the errors thereof are more universal, and therefore more prejudicial to the society of mankind. These I have selected out of many; and having turned over divers casuists, have pitched upon those decisions which I hold most conformable to enlightened reason and religion; sometimes I follow them, and sometimes I leave them for a better guide." He divides his work into four parts,—Cases of profit and traffic, Cases of life and liberty, Cases of piety and religion, and Cases matrimonial; under each of these solving a number of questions, or rather giving a number of moral dissertations.
Casuistry, as a systematic perversion of Christian morality, is now, in the Protestant world, very much unknown: though there still is, and perhaps always will be, that softening down of the strict rules of duty, to which mankind are led either by self-deceit, or by the natural desire of reconciling, with the hope of the divine favour, considerable obliquity from that path of rectitude and virtue which alone is acceptable to God. But the most striking specimen of the length to which casuistry was carried, and of the dangerous consequences which resulted from it, is furnished by the history of the maxims and sentiments of the Jesuists, that celebrated order, which combined with profound literature, and the most zealous support of Popery, an ambition that perverted their understandings, or rather induced them to employ their rational powers in the melancholy work of poisoning the sources of morality, and of casting the name and the appearance of virtue over a dissoluteness of principle and a profligacy of licentiousness, which, had they not been checked by sounder views, and by feelings and habits favourable to morality, would have spread through the world the most degrading misery. See Jesuits .
Charles Buck Theological Dictionary 
The doctrine and science of conscience and its cases, with the rules and principles of resolving the same; drawn partly from natural reason or equity, and partly from the authority of Scripture, the canon law, councils, fathers, &c. To casuistry belongs the decision of all difficulties arising about what a man may lawfully do or not do; what is sin or not sin; what things a man is obliged to do in order to discharge his duty, and what he may let alone without breach of it. Some suppose that all books of casuistry are as useless as they are tiresome. One who is really anxious to do his duty must be very weak, it said, if he can imagine that he has much occasion for them; and with regard to one who is negligent of it, the style of those writings is not such as is likely to awaken him to more attention. The frivolous accuracy which casuists attempt to introduce into subjects which do not admit of it, almost necessarily betray them into dangerous errors; and at the same time render their works dry and disagreeable, abounding in abstruse and metaphysical distinctions, but incapable of exciting in the heart any of those emotions which it is the principal use of books of morality to produce.
On the other hand, I think it may be observed, that, though these remarks may apply to some, they cannot apply to all books of casuistry. It must be acknowledged that nice distinctions, metaphysical reasonings, and abstruse terms, cannot be of much service to the generality, because there are so few who can enter into them; yet, when we consider how much light is thrown upon a subject by the force of good reasoning, by viewing a case in all its bearings, by properly considering all the objections that may be made to it, and by examining it in every point of view; if we consider also how little some men are accustomed to think, and yet at the same time possess that tenderness of conscience which makes them fearful of doing wrong; we must conclude that such works as these, when properly executed, may certainly be of considerable advantage. The reader may consult Ames's Power and Cases of Conscience; Bishop Taylor's Cuctor Dubitantium; Dr. Saunderson's De Obligatione Conscienteae; Pike and Hayward's Cases; and Saurin's Christian Casuistry, in 4th vol. of his Sermons, p. 265, English edition.
Webster's Dictionary 
(1): (a.) Sophistical, equivocal, or false reasoning or teaching in regard to duties, obligations, and morals.
(2): (a.) The science or doctrine of dealing with cases of conscience, of resolving questions of right or wrong in conduct, or determining the lawfulness or unlawfulness of what a man may do by rules and principles drawn from the Scriptures, from the laws of society or the church, or from equity and natural reason; the application of general moral rules to particular cases.
Cyclopedia of Biblical, Theological and Ecclesiastical Literature 
is that branch of Christian morals which treats of cases conscientiae (cases of conscience); that is to say, of questions of conduct in which apparently conflicting duties seem at first to perplex and disturb the moral faculty, and make it necessary to trace, with a careful exclusion of everything but moral considerations, the consequences of the rules of morality (Whewell, History of Moral Ph;losophy, 24). Kant calls caspistry "the dialectics of conscience." In this sense the word might have a good meaning; but its ordinary use is to designate sophistical perversion or evasion of the moral law. Pope supplies examples of both shades of signification, as, first, in the good sense:
"Who shall decide when doctors disagree, And soundest casuists doubt, like you and me?"
Again, in the unfavorable sense:
"Morality by her false guardians drawn, Chicane in furs, and catsutisiry in lawn."
But the theory of "collision of duties," on which this so-called science of casuistry rests, is unsound. Duty is one, though there may be various ways of performing it, and with regard to these, instruction and guidance of course may be needed. What appears to be collision of duties is generally only a collision between duty and inclination. In true Christian ethics, principles of life are set forth, not rules for individual cases. There is nothing like casuistry in the moral teaching of Christ and his apostles. If the "eye be single, the whole body will be full of light;" and if the ultimate aim of man be to do the will of God, this aim, by the aid of the divine Spirit, will clear up all special perplexities as they arise. "When truth must be dealt out in drams or scruples, the health of the soul must be in a very feeble and crazy condition." Bishbop Heber tells us that when Owen was dean of Christ Church, a regular office for the satisfaction of doubtful consciences was held in Oxford, to which the students at last gave the name of "Scruple shop" (Heber's Works of Jeremy Taylor, 1:270). "The cure for diseased consciences is not to be found in a 'scruple shop,' but in the love and care of the great Physician. The law of love, under the guidance of the Holy Spirit, is a solvent of all subordinate moral questions in the practice of life. For the application of this law our reason must be constantly and carefully used" (Wesley, Works, 2:129).
2. Casuistry In The Church Of Rome. — As the Roman doctrines of penance and absolution grew up in the Middle Age, casuistry grew up also, in the form of decisions on special cases of moral difficulty. "The schoolmen delighted in this species of intellectual labor. They transferred their zeal for the most fanciful and frivolous distinctions in what respected the doctrines of religion to its precepts; they anatomized the different virtues; nicely examined all the circumstances by which our estimate of them should be influenced; and they thus rendered the study of morality inextricable, confounded the natural notions of right and wrong, and so accustomed themselves and others to weigh their actions, that they could easily find some excuse for what was most culpable, while they continued under the impression that they were not deviating from what, as moral beings, was incumbent upon them" (Watson, Theol. Dictionary, s.v.). The works which contained collections of cases of conscience, and of which the title commonly was Summa Casuum Conscientice, or something resembling this, were compiled at first for the use of Roman confessors. It was requisite for them to knew, for instance, in what cases penance of a heavier or lighter kind was to be imposed; and what offenses must, for the time, exclude the offender from the communion. The first systematic work on casuistry was that of Raymond of Pennaforti, who published a Summa de Casibus Paenitentialibus, which came into very general use in the 13th century, largely followed by succeeding casuists. In the 14th and 15th centuries the number of such books increased very greatly. "These Summae were in common speech known by certain abbreviated names, borrowed from the name of the author or his birthplace. Thus there was the Astesana, which derived its name from its author, Astesanus, a Minorite of Asti, in Piedmont (Nuremburg, 1482); the Angelica, compiled by Angelus de Clavasio, a Genoese Minorite (Nuremb. 1492); the Pasana or Pisanella, which was also termed Bartholina or Magistruccia (Par. 1470); the Pacifica (Venice, 1574), the Rosella, the Sylvestrina." In these works the subjects were usually arranged alphabetically, and the decisions were given in the form of responses to questions proposed, the opinions being often quoted from or supported by the authority of the Scriptures, or the fathers, or schoolmen. There was no attempt to lay down general principles which might enable the inquirer to determine for himself the matter by which his conscience was disturbed. The lay disciple was supposed to be in entire dependence upon his spiritual teachers for the guidance of his conscience, or, rather, for the determination of the penance and mortification by which his sins were to be obliterated. Moreover, a very large proportion of the offenses which were pointed out in such works were transgressions of the observances required by the Church of those days, and referred to matters of which conscience could not take cognizance without a vary considerable amount of artificial training. Questions of rites and ceremonies were put upon an equal footing with the gravest questions of morals. The Church had given her decision respecting both; and the neglect or violation of her precepts, and of the interpretations of her doctors, could never, it was held, be other than sinful. Thus this body of casuistry was intimately connected with the authority and practices of the Church of Rome, End fell into disuse along with them (Whewell, l. c.).
After the Reformation, the vices of the casuistical system developed themselves in the Church of Rome more fully than ever before. The so- called Moral Theology really poisoned the very fountains of morality. (See Jesuits); (See Pascal). The abb É Maynard published in 1851 a defense of the Jesuits and of their casuistry, under the title Les Provincials Et Leur Refutation (2 vols. 8vo), which is ably reviewed in the Christian Remembrancer (July, 1852), from which we take the following passage: "The first source of the Jesuitical casuistry is to be sought in the inherited habits of thought which had been formed in the Middle-age schools. Conditions, restrictions, distinctions multiplied, of course; but so did the authorities and decisions, inventing doubts, extending liberty, and taking away scruples. Its next cause was the practical need of casuistry (under the Romish system) — the endeavor to fix what cannot be fixed — the limits, in every possible case, of mortal sin. Doubtless moral questions are very important and often very hard. But there are endless questions on which no answer can be given except a bad one — which cannot be answered in the shape proposed at all. We may think it very desirable to be able to state in the abstract, yet for practical use, the extreme cases, which excuse killing, or taking what is not our own; but if we cannot get beyond decisions which leave the door open for unquestionable murders or thefts, or shut it only by vague verbal restrictions, unexplained and inexplicable, about 'prudence,' and 'moderation,' and 'necessity,' and 'gravity of circumstances,' it is a practical illustration of the difficulty of casuistry, which seems to point out that, unless we can do better, we had best leave it alone. But these men were hard to daunt. They could not trust the consciences of mankind with principles of duty, but they could trust without a misgiving their own dialectic forms, as a calculus which nothing could resist. The consequence was twofold.
Their method often did fail, and in the attempt to give exact formulae of right and wrong action, they proved unable to express the right without comprehending the wrong with it. From all evil designs the leaders, at any rate, may be safely absolved; though whether they did not lose their sense of the Peality of human action in the formal terms in which they contemplated it, may be a question. But, though the design of corrupting morality is one of the most improbable charges against any men, the effect may more easily follow, even where not intended. These casuists would not trust the individual conscience, and it had its revenge. They were driven onward till they had no choice left between talking nonsense, or what was worse. They would set conscience to rights in minutest detail, and so they had to take the responsibility of whatever could not be set to rights. Nature outwitted them; it gave up its liberty in the gross, and then forced them to surrender it again in detail. And thus, at length, under the treatment of compilers and abridgers, and under the influence of that idea of authority which deferred to opinions on the same rule as it deferred to testimony — exhibited in the coarsest brevity, and with the affectation of outbidding the boldest precedents — grew up that form of casuistry which is exhibited in the Escobars and Baunys; which, professing to be the indispensable aid to common sense, envelops it in a very Charybdis of discordant opinions; amid whose grotesque suppositions, and whimsical distinctions, and vague yet peremptory rules, bandied about between metaphysics and real life, the mind sinks into a hopeless confusion of moral ideas, and loses every clew to simple and straightforward action."
The principal casuists of the Roman Church are Vasquez ( † 1604), Sanchez ( † 1610), Suarez ( † 1617), Laymann ( † 1635), Filliucius ( † 1622), Bauny ( † 1649), Escobar ( † 1669), Busenbaum ( † 1669). Most of these names are immortalized in Pascal's Provincial Letters (see also each name in its proper place in this Cyclopaedia). See also Migne, Dictionnaire de cas de Conscience (Paris, 1847, 2 vols. 4to). The books of so-called Moral Theology, in the Roman Catholic Church, are generally repertories of casuistry. The most important of them of late are Ligorio, Theologia Moralis (Paris, 1852, 6 vols. 12mo); Gury, Casus Conscientiae (Lyons, 1866, 2 vols. 8vo).
3. Protestant Casuistry. — The Reformation, of course brought the office of such casuistry to an end. "The decision of moral questions was left to each man's own conscience; and his responsibility as to his own moral and spiritual condition could no longer be transferred to others. For himself he must stand or fall. He might, indeed, aid himself by the best lights which the Church could supply — by the counsel of wiser and holier servants of God; and he was earnestly enjoined to seek counsel of God himself by hearty and humble prayer. But he could no longer lean the whole weight of his doubts and his sins upon his father confessor and his mother Church. He must ascertain for himself what is the true and perfect law of God. He could no longer derive hope or satisfaction from the collections of cases, in which the answer rested on the mere authority of men fallible and sinful like himself. Thus the casuistical works of the Romanists lost all weight, and almost all value, in the eyes of the Reformed churches. Indeed, they were looked upon, and justly, as among the glaring evidences of the perversions and human inventions by which the truth of God had been disfigured. But even after the sophistry and the moral perversion connected with casuistry were exploded, the form of that science was preserved, and many valuable moral principles in conformity to it delivered. The writers of the Reformed churches did not at first attempt to substitute anything in the place of the casuistical works of the Romish Church. Besides an aversion to the subject itself, which, as remarked above, they naturally felt, they were, for a considerable period after the Reformation, fully employed upon more urgent objects. If this had not been so, they could not have failed soon to perceive that, in reality, most persons do require some guidance for their consciences, and that rules and precepts, by which men may strengthen themselves against the temptations which cloud the judgment when it is brought into contact with special cases, are of great value to every body of moral and Christian men. But the circumstances of the times compelled them to give their energies mainly to controversies with the Romish and other adversaries, and to leave to each man's own thoughts the regulation of his conduct and feelings." — Whewell, History of Moral Philosophy in England (Lond. 1852, 1 vol. 8vo, p. 28 sq.).
In the writings of the early reformers (e.g. Melancthon and Calvin) there may be found moral directions approaching to casuistry. But the first regular treatise on casuistry in the Protestant Church was Perkins, The whole Treatise of Cases of Conscience, distinguished into three Books (Lond. 1602, 1606; also in his Works, vol. 2, Lond. 1617; in Latin, Hanov. 1603; and in Perkinsii Opera, Geneva, 1624). (See Perkins). He was followed by Henr. Alstedius (Reformed), Theologia Casuum, in 1621 (Hanover, 4to); F. Balduinus, Tract. De Casibus Conscientice (Vitemb. 1628, 4to; Lips. 1684, 4to); Amesius (Ames, q.v.), De Conscientia, ejus jure (t Casibus (Amst. 1630); Osiander, Theologia Casualis (Tubingen, 1680, 8vo). For other writers on casuistry in the Lutheran and Reformed churches, see Walch, Bibliotheca Theologica, vol. 2, cap. 6. In the Church of England we find bishop Hall, Resolutions and Decisions of divers practical Cases of Conscience (Lond. 1649, 8vo); bishop Sanderson, Nine Cases of Conscience (London, 1678, sm. 8vo); Jeremy Taylor, Ductor Dubitantium, or Rule of Conscience (Works, Heber's edition, vols. 12-14). To casuistry belongs also Baxter's Christian Directory, a Sum of Practical Theology (fol. 1673; and in Baxter's Practical Works, vols. 2-6; transl. into German, Frarkf. 1693, 4to). Dickson, professor at Edinburgh, had previously published Therapeutica Sacra (Latin, 1656; English, 1695), a work which Baxter lauds highly. There is still at the University of Cambridge, England, a professorship of Moral Theology or Casuistical Divinity, which was held by the late Dr. Whewell. See Whewell, Lectures on the History of Moral Philosophy in England (Lond. 1852, 8vo); Winer, Theolog. Literatur, vol. 1, § 13, d.; Herzog, Real-Encyklop Ä die, 2:607, 787; Orme, Life of Baxter, vol. 2, ch. 5; Hagenbach, Theolog. Encyklop Ä die, § 94; St Ä udlin, Geschichte der theol. Wissenschaften, 1:342 sq.; Schweitzer, in Studien u. Kritiken, 1850, p. 554; Gass, in hgen's Zeitschrift, 12:152; Bickersteth. Christ. Student, p. 468.