Excerpt of The Spiritual Exercises of St. Ignatius, by Louis J. Puhl, S.J.
    

328. RULES FOR DISCERNMENT OF SPIRITS
II

Further rules for understanding the different movements produced in the soul. They serve for a more accurate discernment of spirits and are more suitable for the second week
  

329.  I.  It is characteristic of God and His Angels, when they act upon the soul, to give true happiness and spiritual joy, and to banish all the sadness and disturbances which are caused by the enemy.
   It is characteristic of the evil one to fight against such happiness and consolation by proposing fallacious reasonings, subtilties, and continual deceptions.

330.  2.  God alone can give consolation to the soul without any previous cause. It belongs solely to the Creator to come into a soul, to leave it, to act upon it, to draw it wholly to the love of His Divine Majesty. I said without previous cause, that is, without any preceding perception or knowledge of any subject by which a soul might be led to such a consolation through its own acts of intellect and will.

331.  3.  If a cause precedes, both the good angel and the evil spirit can give consolation to a soul, but for a quite different purpose. The good angel consoles for the progress of the soul, that it may advance and rise to what is more perfect. The evil spirit consoles for purposes that are the contrary, and that afterwards he might draw the soul to his own perverse intentions and wickedness.

332.  4.  It is a mark of the evil spirit to assume the appearance of an angel of light. He begins by suggesting thoughts that are suited to a devout soul, and ends by suggesting his own. For example, he will suggest holy and pious thoughts that are wholly in conformity with the sanctity of the soul. Afterwards, he will endeavor little by little to end by drawing the soul into his hidden snares and evil designs.

333.  5.  We must carefully observe the whole course of our thoughts. If the beginning and middle and end of the course of thoughts are wholly good and directed to what is entirely right, it is a sign that they are from the good angel. But the course of thoughts suggested to us may terminate in something evil, or distracting, or less good than the soul had formerly proposed to do. Again, it may end in what weakens the soul, or disquiets it; or by destroying the peace, tranquility, and quiet which it had before, it may cause disturbance to the soul. These things are a clear sign that the thoughts are proceeding from the evil spirit, the enemy of our progress and eternal salvation.

334.  6.  When the enemy of our human nature has been detected and recognized by the trail of evil marking his course and by the wicked end to which he leads us, it will be profitable for one who has been tempted to review immediately the whole course of the temptation. Let him consider the series of good thoughts, how they arose, how the evil one gradually attempted to make him step down from the state of spiritual delight and joy in which he was, till finally he drew him to his wicked designs. The purpose of this review is that once such an experience has been understood and carefully observed, we may guard ourselves for the future against the customary deceits of the enemy.

335.  7.  In souls that are progressing to greater perfection, the action of the good angel is delicate, gentle, delightful. It may be compared to a drop of water penetrating a sponge.
    The action of the evil spirit upon such souls is violent, noisy, and disturbing. It may be compared to a drop of water falling upon a stone.
    In souls that are going from bad to worse, the action of the spirits mentioned above is just the reverse. The reason for this is to be sought in the opposition or similarity of these souls to the different kinds of spirits. When the disposition is contrary to that of the spirits, they enter with noise and commotion that are easily perceived. When the disposition is similar to that of the spirits, they enter silently, as one coming into his own house when the doors are open.

336.  8.  When consolation is without previous cause, as was said, there can be no deception in it, since it can proceed from God our Lord only. But a spiritual person who has received such a consolation must consider it very attentively, and must cautiously distinguish the actual time of the consolation from the period which follows it. At such a time the soul is still fervent and favored with the grace and aftereffects of the consolation which has passed. In this second period the soul frequently forms various resolutions and plans which are not granted directly by God our Lord. They may come from our own reasoning on the relations of our concepts and on the consequences of our judgments, or they may come from the good or evil spirit. Hence, they must be carefully examined before they are given full approval and put into execution.

end of excerpt of The Spiritual Exercises of St. Ignatius