When he speaks to the universal Church.
The relevant section of the Vatican II Document Lumen Gentium (excerpted from LG 25):
This religious submission of mind and will must be shown in a special way to the authentic magisterium of the Roman Pontiff, even when he is not speaking ex cathedra; that is, it must be shown in such a way that his supreme magisterium is acknowledged with reverence, the judgments made by him are sincerely adhered to, according to his manifest mind and will. His mind and will in the matter may be known either from the character of the documents, from his frequent repetition of the same doctrine, or from his manner of speaking.
For context, feel free to read the whole thing: http://www.vatican.va/archive/hist_councils/ii_vatican_council/documents/vat-ii_const_19641121_lumen-gentium_en.html
If it shows up in the AAS, there is a need to start paying attention. This is the official means of communicating official things, and if the Pope wants religious assent on the point, that is the way to go about it. If he wants people to think and so opts to say thought provoking things in unofficial forums, that is a means of evangelizing but there is not a need to hang on every word (thankfully—I teach theology and have five kids, so I don’t have the time to digest 10,000 words of Papal stuff every week).
Yes, I agree with this. Not every word from a pope is intended as being binding on people, at least on a one off basis. I would say, though, for those following the interview kerfuffle, frequent repetition is an indicator and this pope is repeating a few things a lot, and some of them are worrying to more than a few people. But, that is another thing. As far as religious submission I agree that it does not apply to every word the pontiff utters, but it certainly is not just attached to ex cathedra statements as was stated earlier. That is an all-too common mistake it seems to me.
The relevant section of the Vatican II Document Lumen Gentium (excerpted from LG 25): This religious submission of mind and will must be shown in a special way to the authentic magisterium of the Roman Pontiff, even when he is not speaking ex cathedra; that is, it must be shown in such a way that his supreme magisterium is acknowledged with reverence, the judgments made by him are sincerely adhered to, according to his manifest mind and will. His mind and will in the matter may be known either from the character of the documents, from his frequent repetition of the same doctrine, or from his manner of speaking.
Is this a change from Pre-Vatican II or would you consider it as more of a clarification? I personally don't trust anything from VII onwards unless it is a re-iteration of previous doctrine/dogma/documents. Also, it can be difficult to determine when a statement pertains to "faith" because almost anything he says is at least indirectly related to faith.