When talking about languages, people sometimes say language A understands language B but language B doesn’t understand language A. How can that be?

Question

The way I see it, if one understands another language, it’s because of similarities in syntax, grammar, etymology or what not. But a similarity is by definition bidirectional, is it not? Is the idea that some languages understand other better than they are themselves understood a lie?

In: Other

Answer 1

In addition to cultural reasons (speakers of language A being more exposed to language B than vice versa), a big factor is phonetics. Portuguese people understand spanish, because spanish is open sounding, it’s read exactly as it’s written. Spanish people will understand written portuguese, but not spoken, because it sounds so different to them, and uses sounds they just don’t have in their language.