this sacrament, so as to make a
man guilty of the body and blood of the Lord: but should it be with
mortal sin, it prevents it of necessity.

For such illusions on the part of demons sometimes come from one's
not striving to receive fervently; and this can be either a mortal or
a venial sin. At other times it is due to malice alone on the part of
the demons who wish to keep men from receiving this sacrament. So we
read in the Conferences of the Fathers (Cassian, Collat. xxii) that
when a certain one always suffered thus on those feast-days on which
he had to receive Communion, his superiors, discovering that there
was no fault on his part, ruled that he was not to refrain from
communicating on that account, and the demoniacal illusion ceased.

In like fashion previous evil thoughts can sometimes be without any
sin whatever, as when one has to think of such things on account of
lecturing or debating; and if it be done without concupiscence and
delectation, the thoughts will not be unclean but honest; and yet
defilement can come of such thoughts, as is clear from the authority
of Augustine (Obj. 1). At other times such thoughts come of
concupiscence and delectation, and should there be consent, it will
be a mortal sin: otherwise it will be a venial sin.

In the same way too the corporeal cause can be without sin, as when
it arises from bodily debility, and hence some individuals suffer
seminal loss without sin even in their wakeful hours; or it can come
from the abundance of nature: for, just as blood can flow without
sin, so also can the semen which is superfluity of the blood,
according to the Philosopher (De Gener. Animal. i). But occasionally
it is with sin, as when it is due to excess of food or drink. And
this also can be either venial or mortal sin; although more
frequently the sin is mortal in the case of evil thoughts on account
of the proneness to consent, rather than in the case of consumption
of food and drink. Hence Gregory, writing to Augustine, Bishop of the
English (Regist. xi), says that one ought to refrain from Communion
when this arises from evil thoughts, but not when it arises from
excess of food or drink, especially if necessity call for Communion.
So, then, one must judge from its cause whether such bodily
defilement of necessity hinders the receiving of this sacrament.

At the same time a sense of decency forbids Communion on two
accounts. The first of these is always verified, viz. the bodily