an know that he has grace. For certitude
about a thing can only be had when we may judge of it by its proper
principle. Thus it is by undemonstrable universal principles that
certitude is obtained concerning demonstrative conclusions. Now no
one can know he has the knowledge of a conclusion if he does not know
its principle. But the principle of grace and its object is God, Who
by reason of His very excellence is unknown to us, according to Job
36:26: "Behold God is great, exceeding our knowledge." And hence His
presence in us and His absence cannot be known with certainty,
according to Job 9:11: "If He come to me, I shall not see Him; if He
depart I shall not understand." And hence man cannot judge with
certainty that he has grace, according to 1 Cor. 4:3, 4: "But neither
do I judge my own self . . . but He that judgeth me is the Lord."

Thirdly, things are known conjecturally by signs; and thus anyone may
know he has grace, when he is conscious of delighting in God, and of
despising worldly things, and inasmuch as a man is not conscious of
any mortal sin. And thus it is written (Apoc. 2:17): "To him that
overcometh I will give the hidden manna . . . which no man knoweth,
but he that receiveth it," because whoever receives it knows, by
experiencing a certain sweetness, which he who does not receive it,
does not experience. Yet this knowledge is imperfect; hence the
Apostle says (1 Cor. 4:4): "I am not conscious to myself of anything,
yet am I not hereby justified," since, according to Ps. 18:13: "Who
can understand sins? From my secret ones cleanse me, O Lord, and from
those of others spare Thy servant."

Reply Obj. 1: Those things which are in the soul by their physical
reality, are known through experimental knowledge; in so far as
through acts man has experience of their inward principles: thus when
we wish, we perceive that we have a will; and when we exercise the
functions of life, we observe that there is life in us.

Reply Obj. 2: It is an essential condition of knowledge that a man
should have certitude of the objects of knowledge; and again, it is
an essential condition of faith that a man should be certain of the
things of faith, and this, because certitude belongs to the
perfection of the intellect, wherein these gifts exist. Hence,
whoever has knowledge or faith is certain that he has them. But it is
otherwise with grace and charity and such like, which perfect the
appetitive faculty.

Reply Obj. 3: Si