All moral conduct may be summed up in the rule: avoid evil and do good. In the language of Christian asceticism, spirits, in the broad sense, is the term applied to certain complex influences, capable of impelling the will, the ones toward good, the others toward evil; we have the wordly spirit of error, the spirit of race, the spirit of Christianity, etc. However, in the restricted sense, spirits indicate the various spiritual agents which, by their suggestions and movements, may influence the moral value of our acts.

Here we shall speak only of this second kind. They are reduced to four, including, in a certain way, the human soul itself, because in consequence of the original Fall, its lower faculties are at variance with its superior powers. Concupiscence, that is to say, disturbances of the imagination and errors of sensibility, thwart or pervert the operations of the intellect and will, by deterring the one from the true and the other from the good (Genesis 8:21; James 1:14). In opposition to our vitiated nature, or so to speak, to the flesh which drags us into sin, the Spirit of God acts within us by grace, a supernatural help given to our intellect and will to lead us back to good and to the observance of the moral law (Romans 7:22-25). Besides these two spirits, the human and the Divine, in the actual order of Providence, two others must be observed. The Creator willed that there should be communication between angels and men, and as the angels are of two kinds, good and bad, the latter try to win us over to their rebellion and the former endeavour to make us their companions in obedience. Hence four spirits lay siege to our liberty: the angelic and the Divine seeking its good, and the human (in the sense heretofore mentioned) and the diabolical its misery. In ordinary language they may, for brevity sake, be called simply the good and the evil spirit.

"Discernment of spirits" is the term given to the judgment whereby it is possible to determine from what spirit the impulses of the soul emanate, and it is easy to understand the importance of this judgment both for self-direction and the direction of others. Now this judgment may be formed in two ways. In the first case the discernment is made by means of an intuitive light which infallibly discovers the quality of the movement; it is then a gift of God, a grace gratis data, vouchsafed mainly for the benefit of our neighbour (1 Corinthians 12:10). This charisma or gift was granted in the early Church and in the course of the lives of the saints as, for example, St. Philip Neri. Second, discernment of spirits may be obtained through study and reflection. It is then an acquired human knowledge, more or less perfect, but very useful in the direction of souls. It is procured, always, of course, with the assistance of grace, by the reading of the Holy Bible, of works on theology and asceticism, of autobiographies, and the correspondence of the most distinguished ascetics. The necessity of self-direction and of directing others, when one had charge of souls, produced documents, preserved in spiritual libraries, from the perusal of which one may see that the discernment of spirits is a science that has always flourished in the Church. In addition to the special treatises enumerated in the bibliography the following documents may be cited for the history of the subject:

the "Shepherd of Hermas" (1, II, Mand. VI, c. 2);
St. Anthony's discourse to the monks of Egypt, in his life by St. Anthanasius;
the "De perfectione spirituali" (ch. 30-33) by Marcus Diadochus;
the "Confessions" of St. Augustine;
St. Bernard's XXIII sermon, "De discretione spirituum";
Gerson's treatise, "De diversis diaboli tentationibus";
St. Theresa's autobiography and "Castle of the Soul";
St. Francis de Sales' letters of direction, etc.

An excellent lesson is that given by St. Ignatius Loyola in his "Spiritual Exercises". Here we find rules for the discernment of spirits and, being clearly and briefly formulated, these rules indicate a secure course, containing in embryo all that is included in the more extensive treatises of later date. For a complete explanation of them the best commentaries on the "Exercises" of St. Ignatius may be consulted. Of the rules transmitted to us by a saint inspired by Divine light and a learned psychologist taught by personal experience, it will suffice to recall the principal ones. Ignatius gives two kinds and we must call attention to the fact that in the second category, according to some opinions, he sometimes considers a more delicate discernment of spirits adapted to the extraordinary course of mysticism. Be that as it may, he begins by enunciating this clear principle, that both the good and the evil spirit act upon a soul according to the attitude it assumes toward them. If the evil spirits pose as their friend, they flatter it; if to resist them, they torment it. But the evil spirit speaks only to the imagination and the senses, whereas the good spirit acts upon reason and conscience. The evil labours to excite concupiscence, the good to intensify love for God. Of course it may happen that a perfectly well-disposed soul suffers from the attacks of the devil deprived of the sustaining consolations of the good angel; but this is only a temporary trial the passing of which must be awaited in patience and humility. St. Ignatius also teaches us to distinguish the spirits by their mode of action and by the end they seek. Without any preceding cause, that is to say, suddenly, without previous knowledge or sentiment, God alone, by virtue of His sovereign dominion, can flood the soul with light and joy. But if there has been a preceding cause, either the good or the bad angel may be the author of the consolation; this remains to be judged from the consequences. As the good angel's object is the welfare of the soul and the bad angel's its defects or unhappiness, if, in the progress of our thoughts all is well and tends to good there is no occasion for uneasiness; on the contrary, if we perceive any deviation whatsoever towards evil or even a slight unpleasant agitation, there is reason to fear. Such, then, is the substance of these brief rules which are nevertheless so greatly admired by the masters of the spiritual life. Although requiring an authorized explanation, when well understood, they act as a preservative against many illusions.

Bibliography Information
Obstat, Nihil. Lafort, Remy, Censor. Entry for 'Discernment of Spirits'. The Catholic Encyclopedia. https://www.studylight.org/encyclopedias/eng/tce/d/discernment-of-spirits.html. Robert Appleton Company. New York. 1914.

Bible Encyclopedias Discernment of Spirits

The Catholic Encyclopedia

Bible Encyclopedias
Discernment of Spirits