What changes from one level to the next
A1: sounds, the article and the present tense
The first level starts with what nothing else prepares you for: Catalan's own letters and sounds, the seven stressed vowels and the neutral vowel. Then come the pieces of any sentence: greeting and introducing yourself, the article —which in central Catalan also goes in front of people's names—, feminine and plural, “ser”, “estar” and “haver-hi”, the present tense of verbs, asking and saying no, numbers and the time, possessives, and the pair “anar” and “venir”, which work more like English “go” and “come” than like Spanish “ir” and “venir”.
What tends to catch people by surprise at this level are details that look whimsical and aren't: “la Marta” with an article, “l'home” with an apostrophe but “la universitat” without one, “ja vinc” (“I'm coming”) when someone calls you, where Spanish says “ya voy”, or the time told in quarters, “un quart de deu”, literally “a quarter of ten”, for quarter past nine. All of that already comes up at A1 because you hear it from day one in any conversation, and leaving it for later only lets the wrong habit settle in.
A2: telling what happened
The second level is the one for verb tenses, and the first of them is the most misleading: the periphrastic past. “Vaig menjar” looks like “I'm going to eat” and means “I ate”. It's the everyday past tense of the spoken language, and alongside it come the present perfect, “he menjat”, for what is still open, the imperfect for describing, and the future. With them come the direct and indirect object weak pronouns, prepositions, “m'agrada” and talking about likes, the imperative, comparisons and obligation.
At this level you move from single sentences to holding a short conversation: saying what you did at the weekend, ordering in a restaurant, complaining about something in a shop. The typical A2 trap is translating word for word from the language you think in. “Tinc que treballar”, copied from Spanish “tengo que”, instead of “he de treballar”, or “vaig menjar” meant as “I'm going to eat”, sound natural to someone thinking in another language and give you away at once. That's why the explanations compare with Spanish, and with English where it helps, and point out where the languages part ways.
B1: “en”, “hi” and the subjunctive
The third level is where Catalan structure stops looking like what you know. The pronouns “en” and “hi” stand in for complements that English and Spanish leave out or repeat: “En vols?” is “do you want some (of it)?”, and “Hi vaig demà”, “I'm going (there) tomorrow”. Then they combine with the other pronouns —“l'hi”, “me'n”, “n'hi”—, which is one of the last things you master. Alongside them come the present subjunctive, the conditional for asking politely, relative clauses, verbal periphrases and connectors.
The level closes with two very practical units: reporting what someone else said, with the changes of tense and pronoun that it brings, and the false friends between Catalan and Spanish, which have already turned up by this point and are worth sorting out. People who reach B1 understanding almost everything tend to get stuck here when speaking, because pronouns are slow to think through and conversation moves fast. The way out isn't memorising tables but repeating lots of set phrases that contain them until they come out on their own: “n'hi ha prou” (“that's enough”), “no hi ha res” (“there's nothing”), “hi estic d'acord” (“I agree”).
B2: registers, varieties and street Catalan
The fourth level polishes what already works. Here come the imperfect subjunctive and unreal situations (“si fos ric…”, “if I were rich…”), the simple past you read in books (“parlà”) even though it's hardly ever said, the passive and impersonal sentences with “es”, and clauses of condition, concession and purpose. These are structures you understand early and use late: they're mainly for writing precisely and for following a formal text, a news story or a letter from the town hall without getting lost.
The other half of B2 looks beyond the classroom: when to address people as “tu”, “vostè” or “vós”, how Balearic and Valencian differ from central Catalan, idioms and sayings, and the Catalan people really speak, with its filler words and its barbarisms, the non-standard borrowings. It isn't there so you imitate what isn't correct, but so you understand what you hear in the street, in a series or among friends, and can tell it apart from what you should say in an interview or in writing.