Bare adverb

From Teflpedia

A bare adverb (/beər ædvɜ:b/) or flat adverb (/flæt ædvɜ:b/) is an adverb that is identical to its equivalent adjective, i.e. it does not follow the rule "add -ly for adverb formation".

Common examples include words like "fast", "soon", "far", "straight". Others may be used particularly in informal English:

Compare: Non-standard English: "Does he run quick?" (standard English: "Does he run quickly?"

In some grammar analyses these may be considered irregular; though it's probably better to consider them to be semi-regular.

The history of language change in this area is a bit of a mess.