Are they mutually intelligible?
Enough that in the last 30 years many Catalans make a point to not switch languages when someone adresses them in Spanish. It’s not a dialect; there’s enough differences in grammar, phonetics and vocabulary to make it a separate language, but if you speak Spanish it takes a few days to get acquainted with the few words which are totally different.
Note that Italian and Spanish have a similar level of intelligibility, and it’s based on the same process: Italian and Catalan are closer to Latin, they’re a lot less likely to have words derived from Arabic, Basque or Visigoth - but for almost every Spanish word that’s got an Arabic root, there will very likely be a (quasi)synonim that’s Latin. And many words which Spanish acquired from Latin America were for new foods or objects, so they went from Spanish to Catalan and Italian.
Calling Spanish castellano in Spanish is a recent development, and a political one: it was part of the price paid to get the Catalanists to vote for the Constitution of 1978. Until then, it had been español or lengua castellana, with the term castellano meaning not the language, but the dialect of it spoken in the northern half of Castilla.
Which, as I understand it, could be considered one language.
National Geographic used to have a feature where they’d describe a US Zip Code. One such articles, for a place in Louisiana, had the writer saying that at one point he realized the “French” those people were speaking was much closer to Catalan than to French. That area did, indeed, get a relatively-heavy Catalan population, but if any Catalan has indeed survived it has been through the pressure first of Spanish, later French and finally English; I doubt my Catalan relatives would be able to communicate in it (none of them is what you’d call “mentally flexible”). I don’t have my old NGs here, but I’ll be going home in the next few days and will check out to see if it’s one of those. If I do have it I’ll give you the reference.
There are areas in the Americas where you can find Basque speakers (euskaldunes), but most of them are from 20th century migrations. I understand Montana has a ton of Basques, for example (20th century migrants, they went there to work in farms); I’ve encountered euskaldunes in Costa Rica, descendants of Spanish Civil War refugees. The americans (continent) I’ve met who had Basque lastnames from were old migrations did not speak Basque.
Basque has an additional characteristic: not only is it unintelligible with other languages, but its dialects diverge a lot as well; it is common for euskaldunes to switch mid-conversation to a trade language, which in older times would be erdera (lit. “the other (local) language” or “the language of the others”) and nowadays for Spanish Basques will be either Spanish or batua (“unified”; the official, artificial dialect). Basques in America won’t have batua, they’ll switch to erdera (Spanish, English, French). After a while, a Basque population which originally had several different dialects will end up growing its own dialect, with the same intelligibility problems and with influences from the local erdera.
Never mind. It was a Bill Bryson book so it probably isn’t true.
Here’s Ethnologue’s take on the Ibero-Romance sub-sub-sub-sub-branch of the Romance languages:
http://www.ethnologue.com/show_family.asp?subid=1179-16
Ethnologue is a good but not perfect source on the relationships between the languages of the world. In this case, they say that Portuguese, Galician, and another language called Fala are the three languages in a sub-sub-branch of the Ibero-Romance languages. Because Ethnologue tends to be somewhat of a splitter rather than a lumper, the languages in a branch at the lowest level tend to be close enough that there is generally a little bit of mutual intelligibility, although it tends to be quite difficult for the speakers of those languages to understand each other. Spanish and three other languages are in a separate sub-sub-branch. Asturian and another language is another sub-sub-branch. Catalan is in another sub-branch. Occitan is in another sub-branch.
If you can learn it in a few days, I wouldn’t call it a separate language. But again, there is not an objective way to determine when two closely related dialects become distinct languages. As I said earlier, it’s as much a political question as a linguistic one.
You can not learn it in a few days, what you can learn in a few days are those words which are completely different. You go from having to ask “uh, sorry? what does naltro mean?” every fifteen minutes to being able to understand. If you consider that being able to understand a language when spoken at normal to slow speeds means that you know it, you sure have different definitions than I do. I mean, since I can decipher written Dutch, and understand it by guessing meanings from relationships to English, French or German, do I know Dutch? I wouldn’t claim I do. All I can say in Dutch is danku, I can’t even count.
Being able to speak it correctly takes months to years, depending on what language and accent you started with. It took me about six months with daily lessons in a hospitable environment(1), but my mother is Catalan by any definition, I grew up hearing Catalan in a regular basis and reading it, and I have a northern Spanish accent, close to the accent Catalans have when speaking Spanish.
1: story told before. When I tried to sign up for “Catalan for non-speakers”, the lady asked me “do you understand it?” “yes, b” “but if you say so much as bon dia, anybody who knows you and who has you labeled ‘Castilian’ makes such a fuss you wish the earth will swallow you” “yes! How do you know?” “it’s the problem all of you in the ‘advanced Catalan’ course will have”. It was. About 50 people in two groups, all of us were perfectly able to understand it, but none of us dared speak it because a bon dia turned into “OHMYGODSHESPOKECATALAN!” <— size=11
OK, so I’ve gone through my not-that-fat collection of NatGeos and if that article existed I don’t have it.
I can tell you that the ZIP USA feature started in September 2000; that in July 2001 it featured Delacroix (LA) and talked about the, and I quote, “Canary islanders and other Spaniards sent there between 1778 and 1783 to reinforce Spanish claims”, that Spanish was still the dominant language there in the 1940s but was getting lost at the time the article was published - no reference to either French or Catalan; that in the “Traveler’s Map of Spain and Portugal” published in October 1998 they display the bilingual areas of Spain as monolingual and the monolingual areas as all speaking “Castillian Spanish” (sic) - I’m not sure whether they couldn’t make up their mind whether to call it “Castillian” or “Spanish”, or whether they truly believe that people from Cádiz (locally pronounced Cái) do speak the Castillian dialect of Spanish - many Americans believe that there is a huge division between “European” Spanish and “American” Spanish and no division inside those two. According to that map, people from Álava/Araba don’t speak Basque, something which I’m sure would be a surprise to residents of Victoria/Gasteiz, and the parts of Navarre where Basque is spoken don’t include Estella/Lizarra… apparently lizarragans have been lying to the rest of us. I mean, I sort’a trust NatGeo when it comes to describing the US and the pictures are pretty as all get-go in any case, but damn when they miss the target they miss it by lightyears, and I’m not sure how well can they be trusted on any linguistic issue.
ETA: now that I look at the language map more carefully, the Portuguese part takes over bits of Extremadura. Olé!