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He breaths really shallowly

He spoke exceedingly quickly

He walked very slowly

He swam extremely fast

He swam extremely quickly

Do we accept fast as an adverb invariably since dictionaries state it can be an adverb or is quickly preferred?

He is real good.

What about real instead of really? Will real one day be as versatile as fast?

Ta
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Do we accept fast as an adverb invariably since dictionaries state it can be an adverb or is quickly preferred?-- 'Fast' is a standard adverb as well as adjective.

He is real good. What about real instead of really?-- The former is still considered casual.

Will real one day be as versatile as fast?-- How would I know?
Comments  
How would I know?

Good point! I suppose I thought you may be interested in giving your opinion. Or perhaps you have a crystal ball you're not sharing...