Objection 1. It would seem that the operation of contemplation is unfittingly divided into a threefold movement, "circular," "straight," and "oblique" (Div. Nom. iv). For contemplation pertains exclusively to rest, according to (Wisdom 8:1)6, "When I go into my house, I shall repose myself with her." Now movement is opposed to rest. Therefore the operations of the contemplative life should not be described as movements.
Objection 2. Further, the action of the contemplative life pertains to the intellect, whereby man is like the angels. Now Dionysius describes these movements as being different in the angels from what they are in the soul. For he says (Div. Nom. iv) that the "circular" movement in the angel is "according to his enlightenment by the beautiful and the good." On the other hand, he assigns the circular movement of the soul to several things: the first of which is the "withdrawal of the soul into itself from externals"; the second is "a certain concentration of its powers, whereby it is rendered free of error and of outward occupation"; and the third is "union with those things that are above it." Again, he describes differently their respective straight movements. For he says that the straight movement of the angel is that by which he proceeds to the care of those things that are beneath him. On the other hand, he describes the straight movement of the soul as being twofold: first, "its progress towards things that are near it"; secondly, "its uplifting from external things to simple contemplation." Further, he assigns a different oblique movement to each. For he assigns the oblique movement of the angels to the fact that "while providing for those who have less they remain unchanged in relation to God": whereas he assigns the oblique movement of the soul to the fact that "the soul is enlightened in Divine knowledge by reasoning and discoursing." Therefore it would seem that the operations of contemplation are unfittingly assigned according to the ways mentioned above.
Objection 3. Further, Richard of St. Victor (De Contempl. i, 5) mentions many other different movements in likeness to the birds of the air. "For some of these rise at one time to a great height, at another swoop down to earth, and they do so repeatedly; others fly now to the right, now to the left again and again; others go forwards or lag behind many times; others fly in a circle now more now less extended; and others remain suspended almost immovably in one place." Therefore it would seem that there are only three movements of contemplation.
On the contrary, stands the authority of Dionysius (Div. Nom. iv).
I answer that, As stated above (119, 1, ad 3), the operation of the intellect, wherein contemplation essentially consists, is called a movement, in so far as movement is the act of a perfect thing, according to the Philosopher (De Anima iii, 1). Since, however, it is through sensible objects that we come to the knowledge of intelligible things, and since sensible operations do not take place without movement, the result is that even intelligible operations are described as movements, and are differentiated in likeness to various movements. Now of bodily movements, local movements are the most perfect and come first, as proved in Phys. viii, 7; wherefore the foremost among intelligible operations are described by being likened to them. These movements are of three kinds; for there is the "circular" movement, by which a thing moves uniformly round one point as center, another is the "straight" movement, by which a thing goes from one point to another; the third is "oblique," being composed as it were of both the others. Consequently, in intelligible operations, that which is simply uniform is compared to circular movement; the intelligible operation by which one proceeds from one point to another is compared to the straight movement; while the intelligible operation which unites something of uniformity with progress to various points is compared to the oblique movement.
Reply to Objection 1. External bodily movements are opposed to the quiet of contemplation, which consists in rest from outward occupations: but the movements of intellectual operations belong to the quiet of contemplation.
Reply to Objection 2. Man is like the angels in intellect generically, but the intellective power is much higher in the angel than in man. Consequently these movements must be ascribed to souls and angels in different ways, according as they are differently related to uniformity. For the angelic intellect has uniform knowledge in two respects. First, because it does not acquire intelligible truth from the variety of composite objects; secondly, because it understands the truth of intelligible objects not discursively, but by simple intuition. On the other hand, the intellect of the soul acquires intelligible truth from sensible objects, and understands it by a certain discoursing of the reason.
Wherefore Dionysius assigns the "circular" movement of the angels to the fact that their intuition of God is uniform and unceasing, having neither beginning nor end: even as a circular movement having neither beginning nor end is uniformly around the one same center. But on the part of the soul, ere it arrive at this uniformity, its twofold lack of uniformity needs to be removed. First, that which arises from the variety of external things: this is removed by the soul withdrawing from externals, and so the first thing he mentions regarding the circular movement of the soul is "the soul's withdrawal into itself from external objects." Secondly, another lack of uniformity requires to be removed from the soul, and this is owing to the discoursing of reason. This is done by directing all the soul's operations to the simple contemplation of the intelligible truth, and this is indicated by his saying in the second place that "the soul's intellectual powers must be uniformly concentrated," in other words that discoursing must be laid aside and the soul's gaze fixed on the contemplation of the one simple truth. On this operation of the soul there is no error, even as there is clearly no error in the understanding of first principles which we know by simple intuition. Afterwards these two things being done, he mentions thirdly the uniformity which is like that of the angels, for then all things being laid aside, the soul continues in the contemplation of God alone. This he expresses by saying: "Then being thus made uniform unitedly," i.e. conformably, "by the union of its powers, it is conducted to the good and the beautiful." The "straight" movement of the angel cannot apply to his proceeding from one thing to another by considering them, but only to the order of his providence, namely to the fact that the higher angel enlightens the lower angels through the angels that are intermediate. He indicates this when he says: "The angel's movement takes a straight line when he proceeds to the care of things subject to him, taking in his course whatever things are direct," i.e. in keeping with the dispositions of the direct order. Whereas he ascribes the "straight" movement in the soul to the soul's proceeding from exterior sensibles to the knowledge of intelligible objects. The "oblique" movement in the angels he describes as being composed of the straight and circular movements, inasmuch as their care for those beneath them is in accordance with their contemplation of God: while the "oblique" movement in the soul he also declares to be partly straight and partly circular, in so far as in reasoning it makes use of the light received from God.
Reply to Objection 3. These varieties of movement that are taken from the distinction between above and below, right and left, forwards and backwards, and from varying circles, are all comprised under either straight and oblique movement, because they all denote discursions of reason. For if the reason pass from the genus to the species, or from the part to the whole, it will be, as he explains, from above to below: if from one opposite to another, it will be from right to left; if from the cause to the effect, it will be backwards and forwards; if it be about accidents that surround a thing near at hand or far remote, the movement will be circular. The discoursing of reason from sensible to intelligible objects, if it be according to the order of natural reason, belongs to the straight movement; but if it be according to the Divine enlightenment, it will belong to the oblique movement as explained above (ad 2). That alone which he describes as immobility belongs to the circular movement.
Wherefore it is evident that Dionysius describes the movement of contemplation with much greater fulness and depth.
Source: Summa Theologica (New Advent)