The worst kind of heretic: Pope Leo XIII

The worst kind of heretic is the one who, while teaching mostly true Catholic doctrine, adds a word of heresy, like a drop of poison in a cup of water.

Attr. Pope Leo XIII.

I have left the record of my original search below. The reason I couldn’t find it is that it’s heavily meme-ified. It’s heavily paraphrased from Pope Leo’s Satis Cognitun (9), where the Holy Father is in turn quoting an anonymous author:

There can be nothing more dangerous than those heretics who admit nearly the whole cycle of doctrine, and yet by one word, as with a drop of poison, infect the real and simple faith taught by our Lord and handed down by Apostolic tradition (Auctor Tract. de Fide Orthodoxa contra Arianos).

So it’s sort of him and sort of not.

Original post follows:


  1. Google Search = Pinterest, tumblr, comments boxes, angry blog posts about Pope Francis, no citations, and no posts that I can find from more than a couple years ago.
  2. Wikiquote = only one quotation from Pope Leo XIII, and this isn’t it. There’s not even a list of disputed quotations or a discussion page.
  3. Direct search of Vatican web site: Your search – site:www.vatican.va The worst kind of heretic is the one who, while teaching mostly true … – did not match any documents.
  4. Hit #3 on Google Books is The Stepford Wives (I am not making this up). None of the hits are useful.

Conclusion: fauxtation until someone gives a real source. Sort of authentic.

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