26 For I ask, if what is not known must not be believed, in what way may children do service to their parents, and love with mutual affection those whom they believe not to be their parents? For it cannot, by any means, be known by reason. But the authority of the mother comes in, that it be believed of the father; but of the mother it is usually not the mother that is believed, but midwives, nurses, servants. For she, from whom a son may be stolen and another put in his place, may she not being deceived deceive?
Yet we believe, and believe without any doubt, what we confess we cannot know. For who but must see, that unless it be so, filial affection, the most sacred bond of the human race, is violated by extreme pride of wickedness? For what madman even would think him to be blamed who discharged the duties that were due to those whom he believed to be his parents, although they were not so? Who, on the other hand, would not judge him to deserve banishment, who failed to love those who were perhaps his true parents, through fear lest he should love pretended. Many things may be alleged, whereby to show that nothing at all of human society remains safe, if we shall determine to believe nothing, which we cannot grasp by full apprehension.
Source: On the Profit of Believing (New Advent)