Jst wntd to throw out that technically a mclass chrctr can learn spells based on their multiclass spell slots, as the mclass rules tell you to refer to ur single class for spells knwn and prep, those classes say u can choose spells of any level you have slots 2/2 so technically you could take a 10 Cleric/ 2nd level in Sorc and learn a spell of 6th level from the sorc list. Same with prepped spells, you can only prep a small # but they can be any level you have slots. Probably not intended but wording wise it seems possible.
— KekDaSnek (@KekTheSnek) December 10, 2017
Take another look at the rule. When figuring out spells known, you pretend you’re not a multiclass character. You look only at what’s in the class’s description, including its table.
— Jeremy Crawford (@JeremyECrawford) December 10, 2017
The confusing part is when it says that every time you level up you can change a spell for another one, assuming you have the spell slots to cast it. The bit in multiclassing should not just say: determine what spells you know and can prepare as if you were a single class, but ALSO as if you only had the spell slots of that single class. The rule as written makes you think you should just read the single class rules and then apply them, but those single class rules then refer at times to the table of spells known and at times to: your spell slots… which makes you think you can go back to the multi-class table for that, which would be OP.