Aquinas on the Evaluation of Human Actions



BY William H. Marshner

Christendom College
Front Royal, Virginia
[Reprinted from The Thomist, 59, 3, July, 1995]

Among the questions dealt with in the Prima Secundae are those of what moral goodness “is” and on what basis it is attributed to some human actions but denied of others. Aquinas’s answers are currently a matter of contention between the proportionalists and their critics, as is his answer to the question of how human actions are classified.

The presentation in the Prima Secundae does give rise to problems, thanks in part to Aquinas’s pedagogical procedure. That procedure can be described as bit-by-bit exposition. Rather than set forth his whole view of a topic in one place, in a synthesis of some sort, and applying it piecemeal thereafter as subsequent questions may demand, the Common Doctor keeps his whole view back, exposing no more of it than is needed to resolve the particular issue at stake in a given article. The result of this, quite often, is that qualifications crucial to a fair comprehension of what he holds are scattered over places far removed from each other. Because what he holds on the classification and evaluation of human actions consists of several parts, each complicated, and all connected, his solution is unsuited to bit-by-bit exposition. Genuine doubts as to what the parts are, and how they come together, can arise. The purpose of the present paper is to present a synthesis that lets the whole picture emerge; as it emerges, certain attempts to read Aquinas in a manner supportive of the proportionalist position will be shown to conflict with the design of the whole.

In his premise to qq. 18-20 in the Prima Secundae, Aquinas describes their subject matter as the goodness or badness (bonitas vel malitia) of human actions. These abstract nouns are derived from the corresponding adjectives, “good” and “bad,” and the very first thing Aquinas tells us (in the first sentence of q. 18, a. 1) is that “good” and “bad” are to be asserted of human actions in the same way as they are asserted of other things.[1] So how is that?


If one should take up any item at all — an apple, a shoe — and say that the item is good, would one be purporting only to describe it as it is, or would one be purporting also to evaluate it in light of how it ought to be? Differently posed, does a proposition of the form “x is good” represent a product of speculative reason alone, or does it include an element, at least, from practical reasoning? Recent analytical philosophy is quite clear that the latter option is correct. “Good” and “bad” are terms which express evaluation rather than some sort of disinterested, theoretical description.[2] Aquinas can be read, at least, as holding the same view.

In a text in which he defined a completely general sense of “good” (more general, for example, than just “human good”), he said: ratio boni est quod aliquid sit appetibile.[3] To make out what this dictum means, two remarks are in order. First, the ratio of a term “T” is the reason anything is called T. Aquinas identified it as the aspect of things which the mind grasps and signifies through “T.”[4] He meant the aspect which would be “what it takes” for a thing to merit or verify the term, in case the term is applied to it. Thus the ratio of “good” is what it takes for anything to be called good; and in that sense it is the reason anything is rightly called “good.” Second, appetitus and appetibile are broad terms. The former means any sort of tendency or inclination whatsoever.[5] The latter (the appetibile) refers to anything which has what it takes to satisfy any sort of inclination of any sort of being.[6] So in the dictum at hand (ratio boni est quod aliquid sit appetibile), Aquinas is saying that, vis-a-vis any kind of thing, S, an object or state having what it takes to satisfy an inclination found in S-things is “good” to (or for) S-things.[7]

Now, if there is a kind of being S0 which has only one inclination, the above remarks suffice to say all that can be said about “good” for that kind of being. But for kinds of beings Si which have more than one inclination, there is more to be said. An object or state may have what it takes to satisfy one inclination of an Si-thing but not its others. Such an object or state is only “good to some extent” or “good in some respect.” By contract, an object or state which had what it took to satisfy all the being’s inclination would be good “period.”[8]

Aquinas had inherited a famous thesis to the effect that good is coextensive with being—that is, that “good” would be applicable wherever “exists” is applicable. To make this thesis come out right, Aquinas posited in every being an inclination to stay in being. In that way, for every being, the fact that it exists would satisfy one of its inclinations, so that its sheer being would be, for it, “good in some respect.” [9] By salvaging (even in this way) the coextensivity thesis, Aquinas escaped the “naturalistic fallacy.” That fallacy consists in thinking that goodness is a nature which some things have and others lack.[10] If that view were correct, “good” and “bad” would work like any contrasting pair of descriptive adjectives, such as “colored” and “colorless” or “animate” and “inanimate.” There would then be good beings and bad beings, just as there are animate beings and inanimate ones. And in that case, the class of good beings would be narrower than the class of beings, just as the class of animate beings is narrower than the class of beings. Aquinas rejected all such ideas with the sweeping declaration that good “adds” nothing to being—adds nothing like a form or nature.[11]

This account of “good” comes closer to the topic of human action, of course, as Aquinas leaves behind the very wide use of “good” just discussed and turns to the more familiar use that arises from human experience of the human inclinations. In human beings, the inclinations are managed (or mismanaged) by the will.[12] So the reason we call something “good” is that it is desirable.[13] Again the evaluative rather than disinterestedly descriptive character of “good” in Aquinas is unmistakable. Moreover, “desirable” is ambiguous as between “in some respect” and “period.” Because the will manages all the inclinations in the light of reason, what would satisfy one of my lower inclinations may be desirable at first blush (and so good “in some respect”) and yet may fail to be desirable “all things considered,” that is, in light of my other inclinations, needs, or interests (and so may fail to be desirable “period”). There is thus a potential, at least, for a conflict to arise between the desirability which is just “there already,” prior to a reasoned judgment, and the desirability which consists precisely in a conformity to such judgment.[14] This potential for conflict lends human interest to the difference between the desirability which is the reason we call something good “in that respect” and the desirability which is the reason we call something good “period.” All the more interest attaches to it, when one asks how the reasoned judgment just mentioned, which in man’s case is supposed to make this difference, is itself to be made. How do we reach an overall assessment? How do we compare the desirability (goodness) which a thing may have “in one respect” with its undesirability in some other respect, so as to judge reasonably whether it is desirable or not “all things considered”?

On this topic, the logic of applying “good” according to Aquinas lines up perfectly with some modern accounts of “evaluation” and conflicts with others. Let us look at an account with which he could agree.

In recent thought, an evaluation is a procedure in which items of some kind are compared to certain criteria (“standards”) and are graded on how they measure up. Thus apples are compared to criteria having to do with size, flavor, freshness. Shoes are compared to criteria having to do with style, comfort, durability. Each criterion is applied to the thing by checking some facet or aspect of the thing. If the facet has the feature demanded by a criterion, then the thing has some property which it ought to have. It is as it ought to be, at least in that respect. If the thing (apple or shoe) has every feature demanded by the criteria applied to it, then it is as it ought to be in every respect. It is “all it should be.” If the thing fails to meet some criterion, it is “lacking” in that respect and so is “not all it should be.” After the thing is compared to the criteria by this sort of application (checking of features), the thing is graded, and this grade is its evaluation proper.[15]

Notice that the term “good” (or its opposite) can appear at two different places in this procedure. It can appear at the end as a final grade (whether as one of many grades, like “excellent,” “good,” “fair,” “poor,” etc., or as one of only two, like “good”/ “bad” in the sense of pass/fail). But it can also appear earlier on, at the feature-checking stage. As each facet of the item is checked against a relevant criterion, satisfactory fulfillment of that criterion can be marked by saying that the item is “good” in that respect (and this preliminary goodness can again be one of many marks or one of only two).

Thus far, the account corresponds exactly to St. Thomas’s discussion of evaluation. “Good” as a final grade he calls bonum simpliciter, and he says in a crucial text that its ratio includes debita plenitudo essendi.[16] This last translates exactly as “all it should be.” So the reason we grade anything as “good” is that it is all it should be.[17]“Good” as a mark on a feature, by contrast, he calls bonum secundum quid.

But now we come to the interesting question, on which varieties of evaluation (and modern accounts of them) divide. The fact that there are two places where the term “good” can appear demands a way of getting from the one to the other. That is, the marks given feature-by-feature must lead somehow to the final grade. One kind of evaluation procedure will sum and average the marks to reach the grade, and so it requires a commensurtion of the features, and one will have had to import enough arithmetic to allow for computation. Another kind of procedure introduces an order of rank among the criteria (or, equivalently, among the features that fulfill criteria), so that if a thing is good in one feature and bad in another, its grade will depend upon whether it is good in any feature that outranks the ones in which it is bad. But it is also possible to have an evaluation procedure without numbers or measures or rankings of any kind.

Such a procedure would be the following. No matter how many features need to be checked, the marks applicable to each feature are just two (“good”/“bad”), and the overall grades are just two (“good”/“bad”), and the rule for getting from the former to the latter is this: the overall grade is “good” if and only if the mark on every required feature is “good”; otherwise, the overall grade is “bad.” (Hence the grade is “bad” if and only if the mark on some feature is not “good.”)

This extremely parsimonious example of an evaluation scheme is of special philosophical interest for three reasons. First, it allows “bad” to be defined entirely by negation. As a final grade, “bad” simply means “not good.” As a mark on a feature, “bad” also means “not good” (so that the ratio of the term is the same in both places) and hence means that the feature demanded is “not there.” Hence the famous neo-Platonic and Patristic thesis that evil is privation — privation of a good, hence absence of a “due” feature—is fully supported.[18]

Secondly, this scheme can be formalized in a modal second-order predicate calculus using only the quantifiers “all” and “some.” An object x of the kind S is graded “good” if and only if, for all predicates ϕ, it ought to be the case that an S-thing is ϕ, and x is ϕ.[19] It follows by elementary logic that an object x of the kind S is graded “not-good” if and only if, for some predicate ϕ, it ought to be the case that an S-thing is ϕ and x is not ϕ.[20] The grade “bad” can then be introduced by definition as “not-good.” Such a formalization confirms that no recourse to rank, number, quantitative, or arithmetical operation on measurements is required.

Thirdly, the parsimonious scheme is explicitly that of Aquinas. His basic rule for getting from the marks to the grade is that a thing is malum simpliciter when it is merely bonum secundum quid (that is, good in some respect but not in every respect). This rule is stated in converse form at ST I, q. 11, a. 2 ad 1: if anything is merely bonum secundum quid, then it is malum simpliciter. But there is no question that he accepts the rule running the other way as well: if anything is malum simpliciter, then it is bonum secundum quid. For he holds that the bad thing at least exists, and that whatever exists is good to that extent (ST I, q. 5, a. 1 ad 1; a. 3 ad 2). For what fails to be good in even that respect is just “nothing” and is not evaluated; if it is not evaluated, it is not “bad.”[21] In many places, Aquinas states the rule in the form in which he found it in his source, Denis: quilibet singularis defectus causat malum, bonum autem causatur ex integra causa.[22] In keeping with this formulation, he says innumerable times that malum is privatio boni.[23] Hence “bad” is defined by negation; “good” and “bad” as grades differ as “all demanded features are there” differs from “some demanded features is not there”, and “good” and “bad” as marks on a facet as “the demanded feature is there” differs from “it is not there.” From mark to grade, the ratio remains constant; “bad” is rigorously defined by negation of “good,” in whose ratio no appeal to rank or measurement is made. Nor is any admissible. For a thing which is good overall has to have no less than every feature demanded by the relevant criteria.


With this background in place, St.Thomas’s opening declaration in I-II, q. 18, a. 1, that “good” and “bad” are to be asserted of human actions in the same way as they are asserted of other things, becomes informative. It allows one to predict much of what the articles in Question 18 will cover. One can predict thatcalling an action good will mean that it is good for man—a good way for a human to act. One can predict that something will be said about the “standards” or “criteria” by which human actions are judged to be good for man. One can predict that the facets upon which these criteria bear will be listed, so that one can see what will need to be checked in evaluating a human action. One can predict that the interesting goodness or badness of human actions—their moral goodness or badness—will be reached via marks on their features, in the parsimonious way already discussed.

These predictions are quickly fulfilled. We are told in article 1 that a human action is not evaluated on the existential basis that it takes place or fails to take place. For, while an action can be called good just for existing (omnis actio, inquantum habet aliquid de esse, intantum habet de bonitate), that talk is irrelevant. For whether the action happens will not turn out to be a feature that is marked in its moral evaluation. Rather, the basis for evaluation is whether the action is “all it should be” as a human action: inquantum vero deficit ei aliquid de plenitudine essendi quae debetur actioni humanae, intantum deficit a bonitate, et sic dicitur mala. We are told that this “all” of what an action should be is not reducible to causal issues like efficacy. For an action will have its causal efficacy through the positive being it has and not through what will make it bad, if it is bad (namely, its lack). The example given is adulterous intercourse, which is highly efficacious towards offspring and yet is not all a human action should be. We are told that what it lacks is “order of reason.”[24] This is a first indication that the criteria for human actions are “ordinations” of reason, so that the features demanded in human actions are conformities to these ordinations. A long way ahead, in I-II, qq. 90ff., we shall be told that the “ordinations” set by reason are universal propositions of practical reason bearing upon actions and having what it takes to be called “laws” (having the ratio legis).[25] We shall be told that these laws or precepts derive from first principles such as “Good is to be done and its opposite avoided”[26] and the Golden Rule[27]; we shall be told that the derivable precepts include the moral content of the Decalogue,[28] and that they therefore include precepts which admit of no exception or “dispensation.”[29]

Thus a human acton will be “good” in case (and only in case)
it is “all it should be” in conforming to precepts derivable by reason.

This conclusion makes sense, because a human action is not so much a good we seek (an object of inclination) as a way of pursuing a good we seek. The “good” actions will be the good ways of pursuing the things we seek. The “good” ways, in turn, will be those which have what it takes to satisfy a desire we have bearing upon our ways of pursuing things. Well, we have various desires bearing on these: we want our ways of pursuing things to be easy (if possible), efficient, enjoyable (if possible), not too tiring, and so on. But controlling all of these preferences, and generating them, is the constant desire which Aquinas calls the natural desire of our will, namely, that our ways of pursuing things make sense, that they be intelligent, that they be reasonable.[30] The features demanded of these ways, therefore, will not be physical features having what it takes to satisfy a drive but conformities-to-reason, having what it takes to satisfy a desire for practical reasonableness.

Next, in articles 2, 3, and 4, we are quickly told which facets of a human action have to be checked to see if the conformities demanded are there. Three facets are listed: genus ex objecto, circumstantiae, finis. These amount respectively to: (1) the specific kind to which the action belongs, when it is classified according to the verb-and-object needed to express what the agent is choosing to do to what, or to whom; (2) the circumstances in which a token of that specific kind would be realized, if the agent were to perform the action as he has chosen; (3) the further purpose (if any) for the sake of which the agent would be choosing to do the action. These three facets are such that each can have the feature of conforming to reason through consistency with a precept of reason, and each can lack this feature; each mark of “good” (or “bad”) means that a conformity-to-precept is there (not there) and hence is a moral mark; and the procedure for getting from the moral marks to the moral grade is just what we should expect—every facet has to be marked “good” (has to conform to precept), or else the action gets “morally bad” for its grade.[31]

  1. Respondeo dicendum quod de bono et malo in actionibus oportet loqui sicut de bono et malo in rebus. …
  2. The analytical philosophers derive a portion of their clarity on this issue from the celebrated remarks of David Hume on the difference between “is” and “ought”: A Treatise on Human Nature, III, i, l.
  3. See ST I, q. 5, q. 1. corpus, and many other places. Aquinas often quoted Aristotle’s definition of “good” as what all things seek or tend toward (appetunt); the Stagirite’s text is in the Nicomachaean Ethics, book I, chapter 1.
  4. Ratio enim significata per nomen est id quod concipit intellectus de re et significat illud per vocem (ST I, q. S, a. 2). Elsewhere, the ratio of a term is more closely identified with its definition (cf. ST I, q. 13, a. 1). The ratio of a term need not be its sense but can just as well be the real aspect of a thing which corresponds to that sense and so fits orverifies the definition.
  5. Aquinas takes appetitus so broadly as to include even gravitational or inertial phenomena. Hence those phenomenologists who prefer to start their account of “good” with admiration are not, in fact, offering a rival starting point. For wherever there is an inclination to admire something, that inclination will be an appetitus.
  6. Among these potential satisfiers Aquinas counts not only objects external to the being, such as food, shelter, etc., but also states internal to it. In biological kinds, the mature state of the individual satisfies tendencies which are present in, but not yet satisfied in, the larval or juvenile state of the individual.
  7. This account coincides with Aristotle’s definition, on the supposition that Aristotle was offering a contextual definition of the phrase “good of,” as in “the good of a stone.” For then he was saying that, for all things x, the good of x = what x seeks or tends toward.Notice that the instrumental sense of “good,” found in “pots are good for cooking,” is set aside by Aristotle and Aquinas as another (and secondary) affair. For pots do not seek cooking; and stones, though good for throwing at malefactors, do not tend towards that employment.Rather, the focal and primary sense of “good” is the sense in which a benefit is good to a beneficiary. Thus an elementary statement of goodness becomes something like “Milk is good for me.” The shorter sentence, “Milk is good,” can then be construed. It is either an abbreviation of “Milk is good for me” or else an implicit generalization of it, meaning that milk is good for my species (people).“It is good for the spider to eat the fly” is ambiguous. Taken one way, it means that eating the fly is good for the spider, which is true for the most part. Taken the other way, it asserts some larger interest in light of which it is good that the spider eat the fly. This larger interest might be the environment, or the global eco-system. Artistotle and Aquinas would have talked about the “common good” of the universe. If this larger system tends or inclines towards a balance in the numbers of the species, and this balance is served by the spider’s (rather often) eating the fly, then the tendency of the system is what makes the spider’s predation “good.” Indirectly, the fact that we humans are part of the system makes the spider’s diet good for us as well.Thus goodness claims which appear theoretical or “absolute” are found to retain a core of intelligibility which is practical and evaluative. A person who literally had no inclinations and who therefore could not experience anything as appetibile could not understand what was meant by any claim of goodness. As we shall see in a moment, claims about the goodness of existence are no exception.
  8. ST I, q. 5, a. 1 ad 1. Aquinas often thought of a thing’s full maturity as a state toward which it was inclined and in which it would find all its inclinations satisfied. Such a state would represent its “perfection” and “complete good.” To reach this state would be the “ultimate purpose” of the thing’s tendings, inclinings, striving, etc. Aquinas affirmed the same connection between “ultimate purpose” and “complete good” in the case of man (ST I-II, q. 1), though he could point to no non-theological or this-worldly state in which all man’s inclinations would be satisfied.
  9. ST I, q. 5, a. 1.
  10. The classic discussion is G. E. Moore, Principia Ethica (Cambridge, 1959), 73.
  11. See ST I, q. 5, a. 3, ad. 1.
  12. … per voluntatem utimur omnibus quae in nobis sunt (ST I, q. 5, a. 4 ad 3).
  13. On the connections and overlaps between appetitus, desiderium, and voluntas, see ST I, q. 19, a. 9; I-II, q. 30, a. 1 ad 2; q. 56, a. 5 ad 1, etc.
  14. According to I-II, q. 50, a. 5 ad 3, the “object” to which the human will is inclined by its very nature is the good which consists in being in accord with reason (bonum rationis); cf I-II. q. 56, a. 6. By this Aquinas underscores the difference between the will (a rational faculty) and the sense appetites. The goodness which is desirability to a sense appetite is pre-rational and may be experienced as counter-rational, that is, as a pull felt in the teeth of rational refusal. But the goodness which is willability is based on reason; it cannot be experienced as against reason, though the accord with reason may be dishonestly contrived through “rationalization.”
  15. I am indebted for this account to J. O. Urmson, “On Grading,” Mind 59 (1950): 145-159.
  16. ST I-II, q. 18, a. 1.
  17. Aquinas does not forget that how-all-the-thing-is becomes how-all-it-should-be (debita plenitudo) by the thing’s having what it takes (in being how-all-it-is) to satisfy the appetitive faculties. This point is made explicit in I-II, q. 18, a. 5 corpus and ad 2.
  18. By contrast, an evaluation procedure which averages the marks has to set an arbitrary number n as the cut-off point, has to define “good” as “higher than or equal to n,” and has to define “bad” as “lower than n.” Thus the ratio of “good” and the ratio of “bad” include relatively opposed relations to n. An evaluation procedure which ranks the criteria has to define the grade “bad” as “lacking an important feature” or “not good in an important respect,” whereas the mark “bad” just means “lacking a feature.” The ranking relation enters, in other words, into the ratio of “good” and “bad” as grades but not into the ratio of “good” and “bad” as marks. Hence the two rationes split apart, even though, in each, “bad” might be defined as “not good.”
  19. In symbols: Sx ⊃ (good x ≡ ∀ϕ(O((y) (Sy ⊃ ϕy)) ⊃ ϕx)), where “O” is a deontic modal operator (“it ought to be the case that”).
  20. That is: Sx ⊃ (~good x ≡ ∃ϕ(O((y) (Sy ⊃ ϕy)). ~ϕx)).
  21. Si vero nihil haberet de entitate vel bonitate, neque malum neque bonum dici posset (ST I-II, q. 18, a. 1). Notice again that the famous slogan, Bonum convertitur cum ente, concerns “good” as a mark on a feature—bonum secundum quid. It has nothing to do with “good” as a final grade, which emphatically does not apply to every being.
  22. Pseudo-Dionysius the Areopagite, De divinis nominibus, chapter 4. See ST I-II, q. a. 4 ad 3, for example.
  23. E.g., ST I, q. 19, a. 9; I-II, q. 18, a. 2 ad 2; q. 21, a. 1.
  24. Ad tertium dicendum quod actio mala potest habere aliquem effectum per se secundum id quod habet de bonitate et entitate. Sicut adulterium est causa generationis humanae inquantum habet commixtionem mans et feminae, non autem inquantum caret ordine rationis (I-II, q. 18, a. 1 ad 3).
  25. I-II, q. 90, a. 1.
  26. I-II, q. 94, a. 2.
  27. I-II, q. 100, a. 3.
  28. Ibid.
  29. I-II, q. 100, a. 8.
  30. See above, note 14.
  31. See I-II, q. 18, a. 4 ad 3.

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