fasting until he partakes of food, consists in a pure
negation, wherefore it cannot be reckoned a virtuous act. Such is
only the fasting of one who abstains in some measure from food for a
reasonable purpose. Hence the former is called natural fasting
(_jejunium jejunii_) [*Literally the 'fast of fasting']: while the
latter is called the faster's fast, because he fasts for a purpose.
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SECOND ARTICLE [II-II, Q. 147, Art. 2]

Whether Fasting Is an Act of Abstinence?

Objection 1: It would seem that fasting is not an act of abstinence.
For Jerome [*The quotation is from the Ordinary Gloss, where the
reference is lacking] commenting on Matt. 17:20, "This kind of devil"
says: "To fast is to abstain not only from food but also from all
manner of lusts." Now this belongs to every virtue. Therefore fasting
is not exclusively an act of abstinence.

Obj. 2: Further, Gregory says in a Lenten Homily (xvi in Evang.) that
"the Lenten fast is a tithe of the whole year." Now paying tithes is
an act of religion, as stated above (Q. 87, A. 1). Therefore fasting
is an act of religion and not of abstinence.

Obj. 3: Further, abstinence is a part of temperance, as stated above
(QQ. 143, 146, A. 1, ad 3). Now temperance is condivided with
fortitude, to which it belongs to endure hardships, and this seems
very applicable to fasting. Therefore fasting is not an act of
abstinence.

_On the contrary,_ Isidore says (Etym. vi, 19) that "fasting is
frugality of fare and abstinence from food."

_I answer that,_ Habit and act have the same matter. Wherefore every
virtuous act about some particular matter belongs to the virtue that
appoints the mean in that matter. Now fasting is concerned with food,
wherein the mean is appointed by abstinence. Wherefore it is evident
that fasting is an act of abstinence.

Reply Obj. 1: Properly speaking fasting consists in abstaining from
food, but speaking metaphorically it denotes abstinence from anything
harmful, and such especially is sin.

We may also reply that even properly speaking fasting is abstinence
from all manner of lust, since, as stated above (A. 1, ad 1), an act
ceases to be virtuous by the conjunction of any vice.

Reply Obj. 2: Nothing prevents the act of one virtue belonging to
another virtue, in so far as it is directed to the end of that
virtue, as explained above (Q. 32, A. 1, ad 2; Q. 85, A. 3).
Accordingly there is no reason why fasting should not be an a