"The sentient appetite is generically one faculty, which is called sensuality; but it is divided into two powers, which are the species of the sentient appetite, viz., the irascible and the concupiscible. To make this clear, one must consider that in natural corruptible things there has to be not only an inclination toward pursuing what is suitable and avoiding what is harmful, but also an inclination toward resisting the corrupting and contrary things that pose an obstacle to what is suitable and that inflict what is harmful ...

"Therefore, since the sentient appetite is an inclination that follows upon sentient apprehension, just as a natural appetite is an inclination that follows upon a natural form, it must be the case that in the sentient part [of the soul] there are two appetitive powers: (i) one through which the soul is simply inclined to pursue those things that are suitable according to the senses and to avoid those things that are harmful, and this is called the concupiscible power; and (ii) a second through which the soul resists opposing things that pose obstacles to what is suitable and that inflict harm, and this is called the irascible power. Hence, the object of the irascible power is said to be the difficult (arduum), because the irascible power tends toward overcoming contraries and winning out over them.

"Moreover, these two inclinations are not reducible to a single principle: (i) For sometimes the soul, in opposition to the inclination of the concupiscible power, inflicts hardships upon itself in order to fight against contraries in accord with the inclination of the irascible power. For this reason, the passions of the irascible power likewise seem to be opposed to the passions of the concupiscible power; for in most cases aroused concupiscence diminishes anger, and aroused anger diminishes concupiscence. (ii) The main point is also clear from the fact that the irascible power is, as it were, a promoter and defender of the concupiscible power when it rises up against obstacles to those suitable things sought by the concupiscible power and fights against the harmful things that the concupiscible power shrinks from. And for this reason all the passions of the irascible power take their origin from passions of the concupiscible power and terminate in the latter. For instance, anger arises from an already inflicted pain and, having gained vengeance, it terminates in joy. It is also for this reason that among animals struggles are over concupiscible things like food and sexual pleasure."

• Question 22: On the subject of the passions of the soul

• 22,1: There are three senses of the term passio (i.e., being acted upon) common in scholastic metaphysics: (1) In the most general sense a passion is simply the passive reception of some form, even if no contrary form is lost by the patient in the process (e.g., air receives light without losing any contrary form). (2) In a less general sense a passion is the passive reception of some form along with the loss of some contrary form; such a passion can be (2a) for the worse (if what is lost was good for the patient) or (2b) for the better (if what is lost was bad for the patient). Passions are in the soul in each of these three ways: (1) In the broad sense of simple passive reception of a form, every instance of the soul's passive reception of a form, even in acts of sentient and intellective cognition, can be called a passion. (2) In the narrower sense of passive reception with a loss, the passions belong to the soul because of bodily transmutations, so that "the passion properly speaking belongs to the soul only per accidens--namely, insofar as the composite is acted upon." Further, the notion of passion is more properly applied to the soul when the transmutation is (2a) for the worse than when it is (2b) for the better, so that "pain (tristitia) is more properly a passion than is joy (laetitia)."

• 22,2: Art. 2 brings us a step closer to a full definition of a passion of the soul by focussing on the question of whether it is the apprehensive (cognitive) part of the soul or the appetitive (affective) part that is the subject of the passions of the soul. The term passion connotes an attraction toward an agent, and it is the appetitive part of the soul, rather than the apprehensive part, that is drawn toward the things that affect the body. "Passions pertain to defect, since they belong to a thing insofar as it is in potentiality. So in those things which approach the First Perfect Being--viz., God--one finds little potentiality and passion, whereas in other things one finds more. And so, too, in the higher part of the soul--viz., the apprehensive part, there is less of passion [than in the appetitive part]." Moreover, the appetitive part is active with respect to exterior acts precisely because it is passively ordered to things in themselves as opposed to things as they exist intentionally in the apprehension. This points to a difference in the corporeal transmutations that lead to apprehension on the one hand and affection on the other. Bodily organs, insofar as they are involved in sentient apprehension, are modified with respect to those intentional properties by virtue of which they are able to play a role in sentient cognition, whereas the bodily changes relevant to sentient appetition are modifications of the natural properties of bodily organs, e.g., their becoming warm or hot, etc.--modifications that are incidental to whatever cognitive roles the bodily organs might have but are essential to their appetitive role. So even though sentient apprehension and sentient appetition both involve acts of corporeal organs, they differ from one another because they are related to different properites of those organs. So a passion of the soul is (materially) a corporeal change, effected by some object, which (i) is received in a bodily organ with respect to its natural properties ["for example, one says that 'anger is an inflammation of the blood around the heart'"] and which (ii) is (formally) ordered back toward the object as it exists in itself.

• 22,3: Passions of the soul, then, are properly found only where there are bodily changes, and so they do not exist in the rational part of the soul or in angels or God. Nonetheless, there are immaterial appetitive acts of will which have effects similar to the effects of the passions, even though they are non-corporeal and hence not themselves passions. For instance, an angel can have joy (gaudium) though not sense pleasure, and higher love (dilectio) though not sense-love.
  

• Question 23: On the differences among the passions

• 23,1-4: St. Thomas here begins his taxonomy of the eleven basic passions, which takes up the whole of question 23. He cites three principles of division:

 
• A. The first division (art. 1) is into the passions of the concupiscible appetite (object=a good or evil qua simply pleasureable or painful) and the passions of the irascible appetite (object=a good qua difficult to obtain or evil qua difficult to avoid).

 
• B. The second division (art. 2) is into passions that are related directly to goods (either simply or qua difficult to obtain) and passions that are related directly to evils (either simply or qua difficult to avoid).

 
• C. The third division (art. 3), which has to do with the inner nature of the passions, is into (i) passions that involve inclinations toward or away from objects, (ii) passions that involve motions toward or away from objects, and (iii) passions that involve the possession (actual or intentional) of objects.

• Given these parameters, plus the added note that anger has no contrary (art. 3), we get the following taxonomy of basic passions of the soul (art. 4):

• Passions of the concupiscible appetite, where the object of the concupiscible power in general is sensible good or sensible evil taken absolutely, i.e., the pleasurable or painful as such:

• 1a. inclination toward a good: amor (love)
• 1b. inclination away from an evil: odium (hate)

• 2a. motion to a possible future good: desiderium/concupiscentia (desire)
• 2b. motion away from a possible future evil: fuga/abominatio (avoidance)

• 3a. possession of a good: delectatio/gaudium/laetitia (pleasure/joy)
• 3b. possession of an evil: dolor/tristitia (pain/sadness)

• Passions of the irascible appetite, where the object of the irascible appetite in general is sensible good insofar as it is difficult to attain and sensible evil insofar as it is difficult to avoid. These passions all presuppose a concupiscible inclination toward the sensible good in question or away from the sensible evil in question:

• 1a. inclination toward a difficult future good qua possible to attain: spes (hope)
• 1b. inclination away from a difficult future good qua impossible to attain: desperatio (despair)

• 2a. inclination away from a difficult future evil qua impossible to overcome: timor (fear)
• 2b. inclination toward a difficult future evil qua possible to overcome: audacia (daring) 

• 3. reaction to a present or past evil qua something to be avenged: ira (anger)

• Question 24: On good and bad in the passions of the soul

• 24,1: Since the passions are not properly human, it might seem that the categories moral good and moral bad do not apply to them. St. Thomas concedes that this is so to the extent that we consider the passions just in themselves. However, we must also consider them insofar as they are subject to the command of reason and will. After all, even our bodily actions can be morally good and bad; and the passions, as St. Thomas puts it, are "even closer to reason and will themselves than the external members are." So the passions admit of moral good and bad insofar as they are voluntary acts of the sentient appetite, and they are voluntary "either by the fact that they are commanded by the will or by the fact that they are not stopped by the will." It is in this sense that human passions differ from animal passions.

• 24,2: Some, such as the Stoics, have seemed to claim that all passions are bad, so that one of the main goals of the moral life is to extinguish the passions. However, if read carefully, they are instead close to the Peripatetics, who said that passions are good when moderated by reason and bad when not so moderated. Summing up in ad 3, St. Thomas says: "Insofar as the passions of the soul go beyond the order of reason, they incline one toward sin, but insofar as they are ordered by reason, they pertain to virtue."

• 24,3: How do the passions enter into acts? Do they make them more good or more bad? Less good or less bad? The passions enhance the goodness of an act to the extent that they are ordered by reason and will to good acts and good ends, but they can also detract from the goodness of a good act. St. Thomas distinguishes two ways in which passions can be related to the judgment of reason; we'll look at them first as they affect good acts:

 
• Antecedently: In this case the passions cloud the judgment of reason and make a good act less good than it would otherwise be. "For it is more praiseworthy to do an act of charity because of the judgment of reason than just from the passion of mercy alone."

 
• Consequently: Here there are two cases:

 
• Case 1: Here the passion spontaneously arises, as it were, because of the intensity with which the good act is willed; and in such a case the passion is a sign of the will's intensity and evinces a greater degree of moral goodness than would otherwise be evinced by the action in the absence of the passion. This would normally be the act of a virtuous person. (Think about the difference between a courageous act undertaken somewhat reluctantly and the same action undertaken with spontaneous enthusiasm.)

 
• Case 2: The will chooses to instigate the passion in order to perform the act more readily. In this case the passion actually adds to the act's goodness. I am about to undertake a courageous action somewhat reluctantly, but deliberately stir up my audacity so that I can do it more readily; this normally involves the active use of my imagination. (Compare the sports dictum: "Let's get ourselves psyched up for this game!!!")

 
• By the same token, one can see that (i) a consequent passion in the sense of case 1 could evince a greater badness of will than the act would otherwise have (a sort of gusto for evil, as it were), and that (ii) a consequent passion in the sense of case 2 could make a bad action a lot worse ("Let's get ourselves psyched up for this armed robbery!!!"). On the other hand, an antecedent passion tends to diminish the badness of an act. (The old "I-don't-know-what-came-over-me" syndrome.)

• 24,4: There are some species of the non-basic passions that are good or bad in their species. For instance, envy [invidia] (sadness at another's good) is bad in its species, whereas modesty or shame [verecundia] (the fear of what is base and disgraceful) is good in its species.
  

• Question 25: The ordering of the passions

• 25, 1-4: A general point is that the passions of the irascible appetite are always ordered to the passions of the concupiscible appetite in such a way that the former have their beginning and end in the latter. That is, they kick in when the going gets tough with respect to getting (avoiding) the objects of the concupiscible passions, and they cease when some object of the concupiscible appetite is possessed (avoided)--anger is complicated because it is preceded by sadness or pain but leads to joy once the evil suffered is avenged or compensated for in some way. There are two relevant ways to order the passions: according to generation or execution and according to completion.

• I. The order of generation or execution (reverse arrows for order of intention):

• amor* (--> odium)
• --> desiderium (--> fuga)
• (--> spes**) (--> desperatio)
• (--> timor) (--> audacia)
• (--> ira)
• --> gaudium (--> tristitia)

• * = the first among the concupiscible passions
• ** = the first among the irascible passions

• II. The order of intention or completion:

• A. Principal passions in the order of completion simpliciter:
• gaudium (where the object is good and present)
• tristitia (where the object is evil and present)

• B. Principal passions in the order of completion with respect to the appetite's motion: 
• spes (where the object is good and future)
• timor (where the object is evil and future)