When I found this page of Pio Nono’s Encyclicals, I got excited, but it’s not in there.
The Syllabus of Errors, as I’ve mentioned before, is essentially a summary of various errors Pius IX condemned in his long pontificate. It is a list of statements that he condemns, so they’re double negatives (i.e., each item listed is wrong). Each item includes a citation of the document it comes from. Liberal Catholics like to say that “Vatican II got rid of that.” RadTrads use the “Syllabus” to claim that certain teachings of Vatican II are, in their view, heretical.
One particular statement for Catholics in America is this one:
“55. The Church ought to be separated from the .State, and the State from the Church. — Allocution “Acerbissimum,” Sept. 27, 1852. “
Now, as a traditional-leaning Catholic, I am more than happy to accept that “separation of Church and State” is a heresy, period. However, I don’t think that’s what His Holiness is saying here.
In official Catholic documents, each word is to be considered in its precise meaning. In this case, he says “ought”. It is *possible* that this statement could be interpreted as condemning a the philosophical principle that Church and State *ought* to be separated, although they can be separated in some instances. It is also important to know what he means here by “separated.” Obviously, the Church maintains to herself the right to advise the State, particularly in matters of Natural Law.
So, the interpretation faithful Catholics have traditionally used to justify our citizenship in America is that the US government cannot, constitutionally, endorse any particular religion. That doesn’t mean that the Church cannot be one of the many voices which influences public policy. However, I want to see the original source material before I make any definitive interpretation of this passage.
The Lewis Crusade 
The text of Acerbissimum is not available, as far as I am aware. However, you might find John Henry Cardinal Newman’s explanation of it helpful. The part where he deals with Establishment of religion -after {284}- is the germane part. Newman says that the pope did not say that separation of church and state is NEVER allowed.
http://www.newmanreader.org/works/anglicans/volume2/gladstone/section7.html
Thank you! Since I originally wrote this, I have found plenty of articles that quote it extensively, explain its context, etc., but many of those are post-Vatican II articles (i.e,. Cardinal Dulles’s article in which he expounds on the hermeneutic of continuity), and so they don’t really help my case with sedevacantists. This would blow some people away.
Dear GodsGadfly,
You can find the original Latin text of Acerbissimum on Google Books if this link works: http://books.google.co.nz/books?id=dgwtAAAAYAAJ&pg=PA59&lpg=PA59&dq=#v=
Look on page 73 or do a search for Acerbissimum in it. The part specifically condemned by article 55 of the Syllabus is on page 76: “Itaque nihil dicimus de illis conceptis decretis, quibus propenebatur, ut Ecclesia nempe a Statu seiungeretur, ut Regularium Ordinum, piorumque Legatorum bona oneri mutuum dandi omnino subiicerentur,” etc. Which (based on my very little Latin) seems to mean: therefore we say nothing of those present decrees, in which it is proposed that the Church really from the State is separated, that Ordinaries and our pious legates ought to altogether pay the burden of this loan, etc.
Yes, the separation of Church and State has been clearly condemned by the Church, since (as Leo XIII says) the two should be related and united like soul and body.