VOA慢速英语:Rethinking Grammar: Who Makes the Rules?

prescriptive grammar – n. a set of rules for using language that are taught, or enforced, so that people will use the language in a particular way.

descriptive grammar – n. a set of rules about language based on how it is actually used. In a descriptive grammar there is no right or wrong language.

linguist – n. a person who studies languages scientifically

no rhyme or reason – idiom. no reason or evidence

arbitrary – adj. not planned or chosen for a particular reason : not based on reason or evidence

double negative – n.  a clause that has two negative words (such as “nothing” and “don't”)

prohibited – adj. not allowed