1 Corinthians 11:18
“For first of all, when you come together in the Church, I hear that divisions exist among you.”
And he says not, “For fear that you do not sup together in common;” “for I hear that you feast in private, and not with the poor:” but what was most calculated thoroughly to shake their minds, that he set down, the name of division, which was the cause of this mischief also: and so he reminded them again of that which was said in the beginning of the Epistle, and was “signified by them of the house of Chloe.” “And I partly believe it.”
Thus, lest they should say, “But what if the accusers speak falsely?” he neither says, “I believe it,” lest he should rather make them reckless; nor again, on the other hand, “I disbelieve it,” lest he should seem to reprove without cause, but, “I partly believe it,” says he, i.e., “I believe it in a small part;” making them anxious and inviting them to return to correction.
Source: Homilies on First Corinthians (New Advent)