Practical syllogisms and incontinence in Thomas Aquinas De malo 3.9, ad 7
Theoretical syllogism
All mammals are animals
All horses are mammals
_________________________
All horses are animals
Theoretical syllogism
All brownies are delicious
This is a brownie
______________________
This brownie is delicious
Practical syllogism
All brownies are delicious
This is a brownie
______________________
I eat this brownie
In practical syllogisms, what is understood but not spelled out is that whatever is delicious is
desirable, and I pursue whatever is desirable (when it is in my reach).
A. (example of Aquinas)
 No fornication is to be committed
 Everything pleasurable is to be enjoyed
Thomas Aquinas, De malo (On Evil), 3.9, ad 7
(see next page).
B. (cf. example of Aristotle)
 Sweet things are harmful
 Sweet things are pleasant
Cf. Aristotle, NE 7.3.1147a23–b5
Temperate person
“considers” /
engages in 
Reason
controls
sense
desire
⇒ reason
determines the
action
Continent person
Incontinent
person
Intemperate
person
“considers” /
engages in 
“considers” / engages in  & 
Reason
brings 
to the
awareness
Sense desire brings
 to the
awareness
Sense
desire
controls
reason
⇒ sense
desire
determines the
action
A.
A.
 No fornication is to be committed
This act is fornication
________________________________
This act is not to be done
 Everything pleasurable is to be enjoyed
This act is pleasurable
____________________________________
This act is to be done
B.
 Sweet things are harmful
This is sweet
____________________
I don’t eat it
B.
 Sweet things are pleasant
This is sweet
___________________
I eat it
Thomas Aquinas, De malo (On Evil), question 3, article 9, reply to objection 7 (trans.: J.
Oesterle, Notre Dame 1993):
“Since an act of sin and of virtue is done by choice, and choice is the desire of what has been
decided on by previous deliberation, and deliberation is a kind of inquiry, it follows that in
every act of virtue or of sin there must be a quasi-syllogistic deduction. But nevertheless the
temperate man syllogizes in one way, the intemperate man in another, the continent man in
one way, the incontinent man in another.
For the temperate man is moved only according to the judgment of reason; hence he
uses a syllogism containing three propositions, making a deduction such as this: No fornication is to be committed, this act is fornication, therefore, this act is not to be done.
But the intemperate man yields entirely to the movement of concupiscence, and so he
too uses a syllogism containing three propositions, making a deduction such as this: everything pleasurable is to be enjoyed, this act is pleasurable, therefore this act is to be done.
However both the continent and the incontinent man are moved in two directions: according to reason to avoid sin, and according to concupiscence to commit sin; but in the
continent man the judgment of reason prevails, in the incontinent man the movement of
concupiscence prevails. Consequently each uses a syllogism having four propositions, but for
contrary conclusions.
For the continent man syllogizes in this manner: No sin is to be committed. And this he
proposes in accordance with the judgment of reason, yet according to the movement of
concupiscence he turns over and over in his mind that everything pleasurable is to be pursued; but because in him the judgment of reason prevails he adopts the first proposition and
concludes under it: this act is a sin, therefore, it is not to be done.
However the incontinent man, in whom the movement of concupiscence prevails, adopts
the second proposition and concludes under it: this is pleasurable, therefore it is to be pursued. And such is properly the man who sins from weakness. And therefore it is evident that
although he may know universally, nevertheless he does not know in particular, because he
does not adopt the premise in keeping with reason but in keeping with concupiscence.”
Ad septimum dicendum, quod cum actus peccati et virtutis sit secundum electionem, electio autem est appetitus praeconsiliati, consilium vero est quaedam inquisitio; necesse est quod in quolibet actu virtutis vel peccati
sit quaedam deductio quasi syllogistica; sed tamen aliter syllogizat temperatus, aliter intemperatus; aliter continens, aliter incontinens. Temperatus enim movetur tantum secundum iudicium rationis; unde utitur syllogismo trium propositionum; quasi sic deducens: nulla fornicatio est committenda, hic actus est fornicatio, ergo
non est faciendus. Intemperatus vero totaliter sequitur concupiscentiam; et ideo etiam ipse utitur syllogismo
trium propositionum, quasi sic deducens: omni delectabili est fruendum, hic actus est delectabilis, ergo hoc est
fruendum. Sed tam continens quam incontinens dupliciter movetur; secundum rationem quidem ad vitandum
peccatum, secundum concupiscentiam vero ad committendum: sed in continente vincit iudicium rationis, in
incontinente vero motus concupiscentiae. Unde uterque utitur syllogismo quatuor propositionum, sed ad
contrarias conclusiones. Continens enim sic syllogizat: nullum peccatum est faciendum; et hoc proponit
secundum iudicium rationis; secundum vero motum concupiscentiae versatur in corde eius quod omne delectabile est prosequendum; sed quia iudicium rationis in eo vincit, assumit et concludit sub primo: hoc est
peccatum; ergo non est faciendum. Incontinens vero, in quo vincit motus concupiscentiae, assumit et concludit sub secundo: hoc est delectabile; ergo est prosequendum; et talis proprie est qui peccat ex infirmitate.
Et ideo patet quod licet sciat in universali, non tamen scit in particulari; quia non assumit secundum rationem,
sed secundum concupiscentiam.