“The pope is a sinful man who makes mistakes. Therefore, he can’t be infallible.”
The premise of this challenge is true; the conclusion is false.
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The pope is a sinful man, but this does not lead to the conclusion that he can’t be infallible. Sinlessness—sometimes called impeccability—operates in a different sphere than infallibility does..
Sinlessness is a quality pertaining to the moral order: it means not making a mistake in the sphere of one’s behavior. Infallibility is a quality pertaining to the doctrinal order: it deals with not making a mistake when proclaiming a doctrine.
The quality of sinlessness is not required for infallibility. One can do sinful things and yet have an accurate understanding. Solomon was supremely wise (see 1 Kings 4:29–34), yet he also sinned greatly (see 1 Kings 11:4–10). The most evil beings there are have an accurate knowledge of God: “Even the demons believe—and shudder” at the prospect of divine judgment (James 2:19).
More to the point, the very first pope—Peter—was a sinful man, but this did not stop him from writing two inspired letters (1 and 2 Peter). Inspiration is a greater charism than infallibility, and it includes infallibility; therefore, even a sinful man like Peter could teach infallibly by God’s grace.
It is also possible for a pope to make mistakes, including of a doctrinal nature—just not when he is teaching under the charism of infallibility.
Again we may look to Peter as an example. His understanding of Christian doctrine was not always perfect. Thus, when Jesus foretold future events, Peter sometimes did not understand or accept the truth of our Lord’s statements (see Matthew 16:21–23, 26:31–35). However, that did not stop him from later writing the inspired, and thus infallible, letters 1 and 2 Peter.
We therefore see that a pope is capable of making mistakes both of the moral and doctrinal order and yet still exercise the charism of infallibility.
God guides the pope, like every validly ordained minister, in the exercise of his ministry—just as he guided Peter. But this does not mean the pope is continuously infallible. The Church does not claim he is, and it would be attacking a straw man to inflate the doctrine of papal infallibility beyond what the Church claims.
By Jimmy Akin