别说【biéshuō】

别说 + X dismisses X as out of the question, and the next clause gives a smaller case Y that doesn't even work. Y comes with 连…都, or with 就是…也.

X and Y can be people as well as things.

The 别说 clause can also come second, closed by 了.

In positive sentences it means "not to mention": Y is already true, so X certainly is.

Which case goes where

X, after 别说, is the bigger or harder case. Y, after 连, is the smaller one. Swapped, the sentence says the opposite of what you mean.

• × 别说英语，我连法语都不会 → 别说法语，我连英语都不会

Not "don't say"

别说 is also simply 别 + 说, "don't say": 别说了 means "stop talking". The "let alone" reading needs the second clause with 连 or 就是.

更不用说 means the same, but it only comes second.